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ORACLE IMP WEBSITES
http://sql-plsql.blogspot.com/2007/03/sql-plsql-resources.html
http://ftp.youngcow.net/doc/oracle10g/appdev.102/b14261/toc.htm
http://mail.tutos.ru/docs/oracle10r2/appdev.101/b10779.pdf
http://www.techonthenet.com/oracle/exceptions
http://www.oracle.com/technology/products/bi/db/10g/pdf/twp_bi_dw_materialized_views_10gr2_0505.pdf
http://www.orafaq.com/wiki/SQL_FAQ
http://www.kalido.com/resource-center-white-papers.htm
ORACLE FAQ’S By PenchalaRaju.Yanamala
Q. What is a Join?
A join is a query that combines rows from two or more tables, views, or materialized views ("snapshots"). Oracle performs a join whenever multiple tables appear in the queries FROM clause. The query’s select list can select any columns from any of these tables. If any two of these tables have a column name in common, you must qualify all references to these columns throughout the query with table names to avoid ambiguity.
Q. What are join conditions?
Most join queries contain WHERE clause conditions that compare two columns, each from a different table. Such a condition is called a join condition. To execute a join, Oracle combines pairs of rows, each containing one row from each table, for which the join condition evaluates to TRUE. The columns in the join conditions need not also appear in the select list.
Q. What is an equijoin?
An equijoin is a join with a join condition containing an equality operator. An equijoin combines rows that have equivalent values for the specified columns.
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Eg:Select ename, job, dept.deptno, dname
From emp, deptWhere emp.deptno = dept.deptno ;
Q. What are self joins?
A self join is a join of a table to itself. This table appears twice in the FROM clause and is followed by table aliases that qualify column names in the join condition.
Eg:SELECT e.ename || ‘ works for ‘ || e2.name “Employees and their Managers”
FROM emp e1, emp e2WHERE e1.mgr = e2.empno;
ENAME EMPNO MGR
BLAKE 12345 67890KING 67890 22446
Result: BLAKE works for KING
Q. What is an Outer Join?
An outer join extends the result of a simple join. An outer join returns all rows that satisfy the join condition and those rows from one table for which no rows from the other satisfy the join condition. Such rows are not returned by a simple join. To write a query that performs an outer join of tables A and B and returns all rows from A, apply the outer join operator (+) to all columns of B in the join condition.For all rows in A that have no matching rows in B, Oracle returns null for any select list expressions containing columns of B. Outer join queries are subject to the following rules and restrictions: The (+) operator can appear only in the WHERE clause or, in the context of
left correlation (that is, when specifying the TABLE clause) in the FROM clause, and can be applied only to a column of a table or view.
If A and B are joined by multiple join conditions, you must use the (+) operator in all of these conditions. If you do not, Oracle will return only the rows resulting from a simple join, but without a warning or error to advise you that you do not have the results of an outer join.
The (+) operator can be applied only to a column, not to an arbitrary expression. However, an arbitrary expression can contain a column marked with the (+) operator.
A condition containing the (+) operator cannot be combined with another condition using the OR logical operator.
A condition cannot use the IN comparison operator to compare a column marked with the (+) operator with an expression.
A condition cannot compare any column marked with the (+) operator with a subquery.
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If the WHERE clause contains a condition that compares a column from table B with a constant, the (+) operator must be applied to the column so that Oracle returns the rows from table A for which it has generated NULLs for this column. Otherwise Oracle will return only the results of a simple join.In a query that performs outer joins of more than two pairs of tables, a single table can be the null-generated table for only one other table. For this reason, you cannot apply the (+) operator to columns of B in the join condition for A and B and the join condition for B and C.
Set Operators: UNION [ALL], INTERSECT, MINUSSet operators combine the results of two component queries into a single result. Queries containing set operators are called compound queries. The number and datatypes of the columns selected by each component query must be the same, but the column lengths can be different.
If you combine more than two queries with set operators, Oracle evaluates adjacent queries from left to right. You can use parentheses to specify a different order of evaluation.
Restrictions: These set operators are not valid on columns of type BLOB, CLOB, BFILE,
varray, or nested table. The UNION, INTERSECT, and MINUS operators are not valid on LONG
columns. To reference a column, you must use an alias to name the column. You cannot also specify the for_update_clause with these set operators. You cannot specify the order_by_clause in the subquery of these operators.
All set operators have equal precedence. If a SQL statement contains multiple set operators, Oracle evaluates them from the left to right if no parentheses explicitly specify another order.
The corresponding expressions in the select lists of the component queries of a compound query must match in number and datatype. If component queries select character data, the datatype of the return values are determined as follows: If both queries select values of datatype CHAR, the returned values have
datatype CHAR.
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If either or both of the queries select values of datatype VARCHAR2, the returned values have datatype VARCHAR2.
Q. What is a UNION?
The UNION operator eliminates duplicate records from the selected rows. We must match datatype (using the TO_DATE and TO_NUMBER functions) when columns do not exist in one or the other table.
Q. What is UNION ALL?
The UNION ALL operator does not eliminate duplicate selected rows.
Note: The UNION operator returns only distinct rows that appear in either result, while the UNION ALL operator returns all rows.
Q. What is an INTERSECT?
The INTERSECT operator returns only those rows returned by both queries. It shows only the distinct values from the rows returned by both queries.
Q. What is MINUS?
The MINUS operator returns only rows returned by the first query but not by the second. It also eliminates the duplicates from the first query.
Note: For compound queries (containing set operators UNION, INTERSECT, MINUS, or UNION ALL), the ORDER BY clause must use positions, rather than explicit expressions. Also, the ORDER BY clause can appear only in the last component query. The ORDER BY clause orders all rows returned by the entire compound query.
Q. How many types of Sql Statements are there in Oracle?
There are basically 6 types of sql statements. They are:
a) Data Definition Language (DDL)The DDL statements define and maintain objects and drop objects.
b) Data Manipulation Language (DML)The DML statements manipulate database data.
c) Transaction Control StatementsManage change by DML
d) Session Control
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Used to control the properties of current session enabling and disabling roles and changing. E.g. Alter Statements, Set Role
e) System Control StatementsChange Properties of Oracle Instance. E.g. Alter System
f) Embedded SqlIncorporate DDL, DML and TCS in Programming Language. E.g. Using the Sql Statements in languages such as 'C', Open, Fetch, execute and close
Q) What is a Transaction in Oracle?
A transaction is a Logical unit of work that compromises one or more SQL Statements executed by a single User. According to ANSI, a transaction begins with first executable statement and ends when it is explicitly committed or rolled back.A transaction is an atomic unit.
Q. What are some of the Key Words Used in Oracle?
Some of the Key words that are used in Oracle are:
a) Committing: A transaction is said to be committed when the transaction makes permanent changes resulting from the SQL statements.
b) Rollback: A transaction that retracts any of the changes resulting from SQL statements in Transaction.
c) SavePoint: For long transactions that contain many SQL statements, intermediate markers or savepoints are declared. Savepoints can be used to divide a transaction into smaller points.
We can declare intermediate markers called savepoints within the context of a transaction. Savepoints divide a long transaction into smaller parts. Using savepoints, we can arbitrarily mark our work at any point within a long transaction. We then have the option later of rolling back work performed before the current point in the transaction but after a declared savepoint within the transaction. For example, we can use savepoints throughout a long complex series of updates so that if we make an error, we do not need to resubmit every statement.
d) Rolling Forward: Process of applying redo log during recovery is called rolling forward.
e) Cursor: A cursor is a handle (name or a pointer) for the memory associated with a specific statement. A cursor is basically an area allocated by Oracle for executing the Sql Statement. Oracle uses an implicit cursor statement for Single row query and Uses Explicit cursor for a multi row query.
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f) System Global Area (SGA): The SGA is a shared memory region allocated by the Oracle that contains Data and control information for one Oracle Instance. It consists of Database Buffer Cache and Redo log Buffer. (KPIT Infotech, Pune)
g) Program Global Area (PGA): The PGA is a memory buffer that contains data and control information for server process.
g) Database Buffer Cache: Database Buffer of SGA stores the most recently used blocks of database data. The set of database buffers in an instance is called Database Buffer Cache.
h) Redo log Buffer: Redo log Buffer of SGA stores all the redo log entries.
i) Redo Log Files: Redo log files are set of files that protect altered database data in memory that has not been written to Data Files. They are basically used for backup when a database crashes.
j) Process: A Process is a 'thread of control' or mechanism in Operating System that executes series of steps.
Q. What are Procedure, functions and Packages?
Procedures and functions consist of set of PL/SQL statements that are grouped together as a unit to solve a specific problem or perform set of related tasks.Procedures do not return values while Functions return one Value.
Packages: Packages provide a method of encapsulating and storing related procedures, functions, variables and other Package Contents
Q. What are Database Triggers and Stored Procedures?
Database Triggers: Database Triggers are Procedures that are automatically executed as a result of insert in, update to, or delete from table.Database triggers have the values old and new to denote the old value in the table before it is deleted and the new indicated the new value that will be used. DT is useful for implementing complex business rules which cannot be enforced using the integrity rules. We can have the trigger as Before trigger or After Trigger and at Statement or Row level.e.g:: operations insert, update ,delete 3 before ,after 3*2 A total of 6 combinations At statement level(once for the trigger) or row level( for every execution ) 6 * 2 A total of 12. Thus a total of 12 combinations are there and the restriction of usage of 12 triggers has been lifted from Oracle 7.3 Onwards.
Stored Procedures: Stored Procedures are Procedures that are stored in Compiled form in the database. The advantage of using the stored procedures is that many users can use the same procedure in compiled and ready to use format.
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Q. How many Integrity Rules are there and what are they?
There are Three Integrity Rules. They are as follows:
a) Entity Integrity Rule: The Entity Integrity Rule enforces that the Primary key cannot be Null
b) Foreign Key Integrity Rule: The FKIR denotes that the relationship between the foreign key and the primary key has to be enforced. When there is data in Child Tables the Master tables cannot be deleted.
c) Business Integrity Rules: The Third Integrity rule is about the complex business processes which cannot be implemented by the above 2 rules.
Q. What are the Various Master and Detail Relationships?
The various Master and Detail Relationship are
a) No Isolated : The Master cannot be deleted when a child is existing
b) Isolated : The Master can be deleted when the child is existingc) Cascading : The child gets deleted when the Master is deleted.
Q. What are the Various Block Coordination Properties?
The various Block Coordination Properties are:
a) Immediate Default Setting. The Detail records are shown when the Master Record are shown.
b) Deferred with Auto QueryOracle Forms defer fetching the detail records until the operator navigates to the detail block.
c) Deferred with No Auto QueryThe operator must navigate to the detail block and explicitly execute a query
Q. What are the Different Optimization Techniques?
The Various Optimization techniques are:
a) Execute Plan: we can see the plan of the query and change it accordingly based on the indexes
b) Optimizer_hint: set_item_property ('DeptBlock',OPTIMIZER_HINT,'FIRST_ROWS');
Select /*+ First_Rows */ Deptno,Dname,Loc,Rowid from dept where (Deptno > 25)
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c) Optimize_Sql: By setting the Optimize_Sql = No, Oracle Forms assigns a single cursor for all SQL statements. This slow downs the processing because for every time the SQL must be parsed whenever they are executed.f45run module = my_firstform userid = scott/tiger optimize_sql = No
d) Optimize_Tp:By setting the Optimize_Tp= No, Oracle Forms assigns seperate cursor only for each query SELECT statement. All other SQL statements reuse the cursor.f45run module = my_firstform userid = scott/tiger optimize_Tp = No
Q. How do u implement the If statement in the Select Statement?
We can implement the if statement in the select statement by using the Decode statement.e.g select DECODE (EMP_CAT,'1','First','2','Second’, Null);
Q. How many types of Exceptions are there?
There are 2 types of exceptions. They are:
a) System Exceptionse.g. When no_data_found, When too_many_rowsb) User Defined Exceptions
e.g. My_exception exceptionWhen My_exception then
Q. What are the inline and the precompiler directives?
The inline and precompiler directives detect the values directly.
Q. How do you use the same lov for 2 columns?
We can use the same lov for 2 columns by passing the return values in global values and using the global values in the code.
Q. How many minimum groups are required for a matrix report?
The minimum number of groups in matrix report is 4.
Q. What is the difference between static and dynamic lov?
The static lov contains the predetermined values while the dynamic lov contains values that come at run time.
Q. What are the OOPS concepts in Oracle?
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Oracle does implement the OOPS concepts. The best example is the Property Classes. We can categorize the properties by setting the visual attributes and then attach the property classes for the objects. OOPS supports the concepts of objects and classes and we can consider the property classes as classes and the items as objects
Q. What is the difference between candidate key, unique key and primary key?
Candidate keys are the columns in the table that could be the primary keys and the primary key is the key that has been selected to identify the rows. Unique key is also useful for identifying the distinct rows in the table.
Q. What is concurrency?
Q. Concurrency is allowing simultaneous access of same data by different users. Locks useful for accessing the database are:
a) Exclusive The exclusive lock is useful for locking the row when an insert, update or delete is being done. This lock should not be applied when we do only select from the row.b) Share lockWe can do the table as Share_Lock and as many share_locks can be put on the same resource.
Q. What are Privileges and Grants?
Privileges are the right to execute a particular type of SQL statements.E.g. Right to Connect, Right to create, Right to resource
Grants are given to the objects so that the object might be accessed accordingly. The grant has to be given by the owner of the object.
Q. What are Table Space, Data Files, Parameter File and Control Files?
Table Space: The table space is useful for storing the data in the database.
When a database is created two table spaces are created.a) System Table space: This data file stores all the tables related to the system and dba tablesb) User Table space: This data file stores all the user related tables
We should have separate table spaces for storing the tables and indexes so that the access is fast.
Data Files: Every Oracle Data Base has one or more physical data files. They store the data for the database. Every data file is associated with only one database. Once the Data file is created the size cannot change. To increase the size of the database to store more data we have to add data file.
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Parameter Files: Parameter file is needed to start an instance.A parameter file contains the list of instance configuration parameters.e.g.db_block_buffers = 500db_name = ORA7db_domain = u.s.acme lang
Control Files: Control files record the physical structure of the data files and redo log filesThey contain the Db name, name and location of dbs, data files, redo log files and time stamp.
Q. Some of the terms related to Physical Storage of the Data.
The finest level of granularity of the data base is the data blocks.
Data Block : One Data Block correspond to specific number of physical database space
Extent : Extent is the number of specific number of contiguous data blocks.
Segments : Set of Extents allocated for Extents. There are three types of Segments.
a) Data Segment: Non Clustered Table has data segment data of every table is stored in cluster data segmentb) Index Segment: Each Index has index segment that stores datac) Roll Back Segment: Temporarily store 'undo' information
Q. What are the Pct Free and Pct Used?
Pct Free is used to denote the percentage of the free space that is to be left when creating a table. Similarly Pct Used is used to denote the percentage of the used space that is to be used when creating a tableE.g. Pctfree 20, Pctused 40
Q. What is Row Chaining?
The data of a row in a table may not be able to fit the same data block. Data for row is stored in a chain of data blocks.
Q. What is a 2 Phase Commit?
Two Phase commit is used in distributed data base systems. This is useful to maintain the integrity of the database so that all the users see the same values. It contains DML statements or Remote Procedural calls that reference a remote object. There are basically 2 phases in a 2 phase commit.
a) Prepare Phase: Global coordinator asks participants to prepare
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b) Commit Phase: Commit all participants to coordinator to Prepared, Read only or abort Reply
A two-phase commit mechanism guarantees that all database servers participating in a distributed transaction either all commit or all roll back the statements in the transaction. A two-phase commit mechanism also protects implicit DML operations performed by integrity constraints, remote procedure calls, and triggers.
Q. What is the difference between deleting and truncating of tables?Deleting a table will not remove the rows from the table but entry is there in the database dictionary and it can be retrieved But truncating a table deletes it completely and it cannot be retrieved.
Q. What are mutating tables?
When a table is in state of transition it is said to be mutating. E.g. If a row has been deleted then the table is said to be mutating and no operations can be done on the table except select.
Q. What are Codd Rules?
Codd Rules describe the ideal nature of a RDBMS. No RDBMS satisfies all the 12 codd rules and Oracle Satisfies 11 of the 12 rules and is the only RDBMS to satisfy the maximum number of rules.
Q. What is Normalization?
Normalization is the process of organizing the tables to remove the redundancy. There are mainly 5 Normalization rules.
1 Normal Form - A table is said to be in 1st Normal Form when the attributes are atomic
2 Normal Form - A table is said to be in 2nd Normal Form when all the candidate keys are dependant on the primary key
3rd Normal Form - A table is said to be third Normal form when it is not dependant transitively
Q. What is the Difference between a post query and a pre query?
A post query will fire for every row that is fetched but the pre query will fire only once.
Q. How can we delete the duplicate rows in the table?
We can delete the duplicate rows in the table by using the Rowid.
Q. Can U disable database trigger? How?
Yes. With respect to table
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ALTER TABLE TABLE [ DISABLE all_trigger ]
Q. What are pseudocolumns? Name them?
A pseudocolumn behaves like a table column, but is not actually stored in the table. You can select from pseudocolumns, but you cannot insert, update, or delete their values. This section describes these pseudocolumns: * CURRVAL * NEXTVAL * LEVEL * ROWID * ROWNUM
Q. How many columns can table have?
The number of columns in a table can range from 1 to 254.
Q. Is space acquired in blocks or extents?
In extents.
Q. What is clustered index?
In an indexed cluster, rows are stored together based on their cluster key values. Can not be applied for HASH.
Q. What are the datatypes supported By oracle (INTERNAL)?
Varchar2, Number, Char, MLSLABEL.
Q. What are attributes of cursor?
%FOUND , %NOTFOUND , %ISOPEN,%ROWCOUNT
Q. Can you use select in FROM clause of SQL select ?
Yes.
Q. Describe the difference between a procedure, function and anonymous pl/sql block.
Candidate should mention use of DECLARE statement, a function must return a value while a procedure doesn’t have to.
Q. What is a mutating table error and how can you get around it?
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This happens with triggers. It occurs because the trigger is trying to modify a row it is currently using. The usual fix involves either use of views or temporary tables so the database is selecting from one while updating the other.
Q. Describe the use of %ROWTYPE and %TYPE in PL/SQL.
%ROWTYPE allows you to associate a variable with an entire table row. The %TYPE associates a variable with a single column type.
Q. What packages (if any) has Oracle provided for use by developers?
Oracle provides the DBMS_ series of packages. There are many which developers should be aware of such as DBMS_SQL, DBMS_PIPE, DBMS_TRANSACTION, DBMS_LOCK, DBMS_ALERT, DBMS_OUTPUT, DBMS_JOB, DBMS_UTILITY, DBMS_DDL, UTL_FILE. If they can mention a few of these and describe how they used them, even better. If they include the SQL routines provided by Oracle, great, but not really what was asked.
Q. Describe the use of PL/SQL tables.
PL/SQL tables are scalar arrays that can be referenced by a binary integer. They can be used to hold values for use in later queries or calculations. In Oracle 8 they will be able to be of the %ROWTYPE designation, or RECORD.
Q. When is a declare statement needed?
The DECLARE statement is used in PL/SQL anonymous blocks such as with stand alone, non-stored PL/SQL procedures. It must come first in a PL/SQL standalone file if it is used.
Q. In what order should a open/fetch/loop set of commands in a PL/SQL block be implemented if you use the %NOTFOUND cursor variable in the exit when statement? Why?
OPEN then FETCH then LOOP followed by the exit when. If not specified in this order will result in the final return being done twice because of the way the %NOTFOUND is handled by PL/SQL.
Q. What are SQLCODE and SQLERRM and why are they important for PL/SQL developers?
SQLCODE returns the value of the error number for the last error encountered. The SQLERRM returns the actual error message for the last error encountered. They can be used in exception handling to report, or, store in an error log table,
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the error that occurred in the code. These are especially useful for the WHEN OTHERS exception.
Q. How can you find within a PL/SQL block, if a cursor is open?
Use the %ISOPEN cursor status variable.
Q. How can you generate debugging output from PL/SQL?
Use the DBMS_OUTPUT package. Another possible method is to just use the SHOW ERROR command, but this only shows errors. The DBMS_OUTPUT package can be used to show intermediate results from loops and the status of variables as the procedure is executed. The new package UTL_FILE can also be used.
Q. What are the types of triggers?
There are 12 types of triggers in PL/SQL that consist of combinations of the BEFORE, AFTER, ROW, TABLE, INSERT, UPDATE, DELETE and ALL key words:
BEFORE ALL ROW INSERTAFTER ALL ROW INSERTBEFORE INSERTAFTER INSERTetc.
Q. How can variables be passed to a SQL routine?
By use of the & or double && symbol. For passing in variables numbers can be used (&1, &2,...,&8) to pass the values after the command into the SQLPLUS session. To be prompted for a specific variable, place the ampersanded variable in the code itself: “select * from dba_tables where owner=&owner_name;” . Use of double ampersands tells SQLPLUS to resubstitute the value for each subsequent use of the variable, a single ampersand will cause a reprompt for the value unless an ACCEPT statement is used to get the value from the user.
Q. You want to include a carriage return/linefeed in your output from a SQL script, how can you do this?
The best method is to use the CHR() function (CHR(10) is a return/linefeed) and the concatenation function “||”. Another method, although it is hard to document and isn’t always portable is to use the return/linefeed as a part of a quoted string.
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Q. How can you call a PL/SQL procedure from SQL?
By use of the EXECUTE (short form EXEC) command. You can also wrap the call in a BEGIN END block and treat it as an anonymous PL/SQL block.
Q. How do you execute a host operating system command from within SQL?
By use of the exclamation point “!” (in UNIX and some other OS) or the HOST (HO) command.
Q. You want to use SQL to build SQL, what is this called and give an example?
This is called dynamic SQL. An example would be:
set lines 90 pages 0 termout off feedback off verify offspool drop_all.sqlselect ‘drop user ‘||username||’ cascade;’ from dba_userswhere username not in (“SYS’,’SYSTEM’);spool off
Essentially you are looking to see that they know to include a command (in this case DROP USER...CASCADE;) and that you need to concatenate using the ‘||’ the values selected from the database.
Q. What SQLPlus command is used to format output from a select?
This is best done with the COLUMN command.
Q. You want to group the following set of select returns, what can you group on?Max(sum_of_cost), min(sum_of_cost), count(item_no), item_no
The only column that can be grouped on is the “item_no” column, the rest have aggregate functions associated with them.
Q. What special Oracle feature allows you to specify how the cost based system treats a SQL statement?
The COST based system allows the use of HINTs to control the optimizer path selection. If they can give some example hints such as FIRST ROWS, ALL ROWS, USING INDEX, STAR, even better.
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Q. You want to determine the location of identical rows in a table before attempting to place a unique index on the table, how can this be done?
Oracle tables always have one guaranteed unique column, the rowid column. If you use a min/max function against your rowid and then select against the proposed primary key you can squeeze out the rowids of the duplicate rows pretty quick. For example:
select rowid from emp ewhere e.rowid > (select min(x.rowid)from emp xwhere x.emp_no = e.emp_no);
In the situation where multiple columns make up the proposed key, they must all be used in the where clause.
Q. What is a Cartesian product?
A Cartesian product is the result of an unrestricted join of two or more tables. The result set of a three table Cartesian product will have x * y * z number of rows where x, y, z correspond to the number of rows in each table involved in the join. This occurs if there are not at least n-1 joins where n is the number of tables in a SELECT.
Q. You are joining a local and a remote table, the network manager complains about the traffic involved, how can you reduce the network traffic?
Push the processing of the remote data to the remote instance by using a view to pre-select the information for the join. This will result in only the data required for the join being sent across.
Q. What is the default ordering of an ORDER BY clause in a SELECT statement?
Ascending
Q. What is tkprof and how is it used?
The tkprof tool is a tuning tool used to determine cpu and execution times for SQL statements. You use it by first setting timed_statistics to true in the initialization file and then turning on tracing for either the entire database via the sql_trace parameter or for the session using the ALTER SESSION command. Once the trace file is generated you run the tkprof tool against the trace file and then look at the output from the tkprof tool. This can also be used to generate explain plan output.
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Q. What is explain plan and how is it used?
The EXPLAIN PLAN command is a tool to tune SQL statements. To use it you must have an explain_table generated in the user you are running the explain plan for. This is created using the utlxplan.sql script. Once the explain plan table exists you run the explain plan command giving as its argument the SQL statement to be explained. The explain_plan table is then queried to see the execution plan of the statement. Explain plans can also be run using tkprof.
Q. How do you set the number of lines on a page of output? The width?
The SET command in SQLPLUS is used to control the number of lines generated per page and the width of those lines, for example SET PAGESIZE 60 LINESIZE 80 will generate reports that are 60 lines long with a line width of 80 characters. The PAGESIZE and LINESIZE options can be shortened to PAGES and LINES.
Q. How do you prevent output from coming to the screen?
The SET option TERMOUT controls output to the screen. Setting TERMOUT OFF turns off screen output. This option can be shortened to TERM.
Q. How do you prevent Oracle from giving you informational messages during and after a SQL statement execution?
The SET options FEEDBACK and VERIFY can be set to OFF.
Q. How do you generate file output from SQL?
By use of the SPOOL command.
Data Modeler:
Q. Describe third normal form?
Expected answer: Something like: In third normal form all attributes in an entity are related to the primary key and only to the primary key
Q. Is the following statement true or false? Why or why not?
“All relational databases must be in third normal form”
False. While 3NF is good for logical design most databases, if they have more than just a few tables, will not perform well using full 3NF. Usually some entities will be denormalized in the logical to physical transfer process.
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Q. What is an ERD?
An ERD is an Entity-Relationship-Diagram. It is used to show the entities and relationships for a database logical model.
Q. Why are recursive relationships bad? How do you resolve them?
A recursive relationship (one where a table relates to itself) is bad when it is a hard relationship (i.e. neither side is a “may” both are “must”) as this can result in it not being possible to put in a top or perhaps a bottom of the table (for example in the EMPLOYEE table you couldn’t put in the PRESIDENT of the company because he has no boss, or the junior janitor because he has no subordinates). These type of relationships are usually resolved by adding a small intersection entity.
Q. What does a hard one-to-one relationship mean (one where the relationship on both ends is “must”)?
This means the two entities should probably be made into one entity.
Q. How should a many-to-many relationship be handled?
By adding an intersection entity table
Q. What is an artificial (derived) primary key? When should an artificial (or derived) primary key be used?
A derived key comes from a sequence. Usually it is used when a concatenated key becomes too cumbersome to use as a foreign key.
Q. When should you consider denormalization?
Whenever performance analysis indicates it would be beneficial to do so without compromising data integrity. Q. What is a Schema?
Associated with each database user is a schema. A schema is a collection of schema objects. Schema objects include tables, views, sequences, synonyms, indexes, clusters, database links, snapshots, procedures, functions, and packages.
Q. What do you mean by table?
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Tables are the basic unit of data storage in an Oracle database. Data is stored in rows and columns.A row is a collection of column information corresponding to a single record.
Q. Is there an alternative of dropping a column from a table? If yes, what?
Dropping a column in a large table takes a considerable amount of time. A quicker alternative is to mark a column as unused with the SET UNUSED clause of the ALTER TABLE statement. This makes the column data unavailable, although the data remains in each row of the table. After marking a column as unused, you can add another column that has the same name to the table. The unused column can then be dropped at a later time when you want to reclaim the space occupied by the column data.
Q. What is a rowid?
The rowid identifies each row piece by its location or address. Once assigned, a given row piece retains its rowid until the corresponding row is deleted, or exported and imported using the Export and Import utilities.
Q. What is a view? (KPIT Infotech, Pune)
A view is a tailored presentation of the data contained in one or more tables or other views. A view takes the output of a query and treats it as a table. Therefore, a view can be thought of as a stored query or a virtual table.
Unlike a table, a view is not allocated any storage space, nor does a view actually contain data. Rather, a view is defined by a query that extracts or derives data from the tables that the view references. These tables are called base tables. Base tables can in turn be actual tables or can be views themselves (including snapshots). Because a view is based on other objects, a view requires no storage other than storage for the definition of the view (the stored query) in the data dictionary.
Q. What are the advantages of having a view?
The advantages of having a view are: To provide an additional level of table security by restricting access to a
predetermined set of rows or columns of a table To hide data complexity To simplify statements for the user To present the data in a different perspective from that of the base table To isolate applications from changes in definitions of base tables To save complex queries
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For example, a query can perform extensive calculations with table information.
By saving this query as a view, you can perform the calculations each time the view is queried.
Q. What is a Materialized View? (Honeywell, KPIT Infotech, Pune)
Materialized views, also called snapshots, are schema objects that can be used to summarize, precompute, replicate, and distribute data. They are suitable in various computing environments especially for data warehousing.From a physical design point of view, Materialized Views resembles tables or partitioned tables and behave like indexes.
Q. What is the significance of Materialized Views in data warehousing?
In data warehouses, materialized views are used to precompute and store aggregated data such as sums and averages. Materialized views in these environments are typically referred to as summaries because they store summarized data. They can also be used to precompute joins with or without aggregations.
Cost-based optimization can use materialized views to improve query performance by automatically recognizing when a materialized view can and should be used to satisfy a request. The optimizer transparently rewrites the request to use the materialized view. Queries are then directed to the materialized view and not to the underlying detail tables or views.
Q. Differentiate between Views and Materialized Views? (KPIT Infotech, Pune)
Q. What is the major difference between an index and Materialized view?
Unlike indexes, materialized views can be accessed directly using a SELECT statement.
Q. What are the procedures for refreshing Materialized views?
Oracle maintains the data in materialized views by refreshing them after changes are made to their master tables. The refresh method can be:
a) incremental (fast refresh) or b) complete
For materialized views that use the fast refresh method, a materialized view log or direct loader log keeps a record of changes to the master tables.
Materialized views can be refreshed either on demand or at regular time intervals.Alternatively, materialized views in the same database as their master tables can be refreshed whenever a transaction commits its changes to the master tables.
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Q. What are materialized view logs?
A materialized view log is a schema object that records changes to a master table’s data so that a materialized view defined on the master table can be refreshed incrementally. Another name for materialized view log is snapshot log.Each materialized view log is associated with a single master table. The materialized view log resides in the same database and schema as its master table.
Q. What is a synonym?
A synonym is an alias for any table, view, snapshot, sequence, procedure, function, or package. Because a synonym is simply an alias, it requires no storage other than its definition in the data dictionary.
Q. What are the advantages of having synonyms?
Synonyms are often used for security and convenience. For example, they can do the following:
1. Mask the name and owner of an object2. Provide location transparency for remote objects of a distributed database3. Simplify SQL statements for database users
Q. What are the advantages of having an index? Or What is an index?
The purpose of an index is to provide pointers to the rows in a table that contain a given key value. In a regular index, this is achieved by storing a list of rowids for each key corresponding to the rows with that key value. Oracle stores each key value repeatedly with each stored rowid.
Q. What are the different types of indexes supported by Oracle?
The different types of indexes are:a. B-tree indexesb. B-tree cluster indexesc. Hash cluster indexesd. Reverse key indexese. Bitmap indexes
Q. Can we have function based indexes?
Yes, we can create indexes on functions and expressions that involve one or more columns in the table being indexed. A function-based index precomputes the value of the function or expression and stores it in the index. You can create a function-based index as either a B-tree or a bitmap index.
Q. What are the restrictions on function based indexes?
The function used for building the index can be an arithmetic expression or an expression that contains a PL/SQL function, package function, C callout, or SQL
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function. The expression cannot contain any aggregate functions, and it must be DETERMINISTIC. For building an index on a column containing an object type, the function can be a method of that object, such as a map method. However, you cannot build a function-based index on a LOB column, REF, or nested table column, nor can you build a function-based index if the object type contains a LOB, REF, or nested table.
Q. What are the advantages of having a B-tree index?
The major advantages of having a B-tree index are:1. B-trees provide excellent retrieval performance for a wide range of
queries, including exact match and range searches.2. Inserts, updates, and deletes are efficient, maintaining key order for fast
retrieval.3. B-tree performance is good for both small and large tables, and does not
degrade as the size of a table grows.
Q. What is a bitmap index? (KPIT Infotech, Pune)
The purpose of an index is to provide pointers to the rows in a table that contain a given key value. In a regular index, this is achieved by storing a list of rowids for each key corresponding to the rows with that key value. Oracle stores each key value repeatedly with each stored rowid. In a bitmap index, a bitmap for each key value is used instead of a list of rowids.Each bit in the bitmap corresponds to a possible rowid. If the bit is set, then it means that the row with the corresponding rowid contains the key value. A mapping function converts the bit position to an actual rowid, so the bitmap index provides the same functionality as a regular index even though it uses a different representation internally. If the number of different key values is small, then bitmap indexes are very space efficient. Bitmap indexing efficiently merges indexes that correspond to several conditions in a WHERE clause. Rows that satisfy some, but not all, conditions are filtered out before the table itself is accessed. This improves response time, often dramatically.
Q. What are the advantages of having bitmap index for data warehousing applications? (KPIT Infotech, Pune)
Bitmap indexing benefits data warehousing applications which have large amounts of data and ad hoc queries but a low level of concurrent transactions. For such applications, bitmap indexing provides:
1. Reduced response time for large classes of ad hoc queries2. A substantial reduction of space usage compared to other indexing
techniques3. Dramatic performance gains even on very low end hardware4. Very efficient parallel DML and loads
Q. What is the advantage of bitmap index over B-tree index?
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Fully indexing a large table with a traditional B-tree index can be prohibitively expensive in terms of space since the index can be several times larger than the data in the table. Bitmap indexes are typically only a fraction of the size of the indexed data in the table.
Q. What is the limitation/drawback of a bitmap index?
Bitmap indexes are not suitable for OLTP applications with large numbers of concurrent transactions modifying the data. These indexes are primarily intended for decision support in data warehousing applications where users typically query the data rather than update it.
Bitmap indexes are not suitable for high-cardinality data.
Q. How do you choose between B-tree index and bitmap index?
The advantages of using bitmap indexes are greatest for low cardinality columns: that is, columns in which the number of distinct values is small compared to the number of rows in the table. If the values in a column are repeated more than a hundred times, then the column is a candidate for a bitmap index. Even columns with a lower number of repetitions and thus higher cardinality, can be candidates if they tend to be involved in complex conditions in the WHERE clauses of queries.
For example, on a table with one million rows, a column with 10,000 distinct values is a candidate for a bitmap index. A bitmap index on this column can out-perform a B-tree index, particularly when this column is often queried in conjunction with other columns.
B-tree indexes are most effective for high-cardinality data: that is, data with many possible values, such as CUSTOMER_NAME or PHONE_NUMBER. A regular Btree index can be several times larger than the indexed data. Used appropriately, bitmap indexes can be significantly smaller than a corresponding B-tree index.
Q. What are clusters?
Clusters are an optional method of storing table data. A cluster is a group of tables that share the same data blocks because they share common columns and are often used together.For example, the EMP and DEPT table share the DEPTNO column. When you cluster the EMP and DEPT tables, Oracle physically stores all rows for each department from both the EMP and DEPT tables in the same data blocks.
Q. What is partitioning? (KPIT Infotech, Pune)
Partitioning addresses the key problem of supporting very large tables and indexes by allowing you to decompose them into smaller and more manageable pieces called partitions. Once partitions are defined, SQL statements can access and manipulate the partitions rather than entire tables or indexes. Partitions are
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especially useful in data warehouse applications, which commonly store and analyze large amounts of historical data.
Q. What are the different partitioning methods?
Two primary methods of partitioning are available: 1. range partitioning, which partitions the data in a table or index
according to a range of values, and 2. hash partitioning, which partitions the data according to a hash
function.
Another method, composite partitioning, partitions the data by range and further subdivides the data into sub partitions using a hash function.
Q. What is the necessity to have table partitions?
The need to partition large tables is driven by: Data Warehouse and Business Intelligence demands for ad hoc analysis
on great quantities of historical data Cheaper disk storage Application performance failure due to use of traditional techniques
Q. What are the advantages of storing each partition in a separate tablespace?
The major advantages are:1. You can contain the impact of data corruption.2. You can back up and recover each partition or subpartition independently.3. You can map partitions or subpartitions to disk drives to balance the I/O
load.
Q. What are the advantages of partitioning?
Partitioning is useful for:1. Very Large Databases (VLDBs)2. Reducing Downtime for Scheduled Maintenance3. Reducing Downtime Due to Data Failures4. DSS Performance5. I/O Performance6. Disk Striping: Performance versus Availability7. Partition Transparency
Q. What is Range Partitioning? (KPIT Infotech, Pune)
Range partitioning maps rows to partitions based on ranges of column values. Range partitioning is defined by the partitioning specification for a table or index:
PARTITION BY RANGE ( column_list )
and by the partitioning specifications for each individual partition:
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VALUES LESS THAN ( value_list )
Q. What is Hash Partitioning?
Hash partitioning uses a hash function on the partitioning columns to stripe data into partitions. Hash partitioning allows data that does not lend itself to range partitioning to be easily partitioned for performance reasons such as parallel DML, partition pruning, and partition-wise joins.Q. What are the advantages of Hash partitioning over Range Partitioning?
Hash partitioning is a better choice than range partitioning when:a) You do not know beforehand how much data will map into a given rangeb) Sizes of range partitions would differ quite substantiallyc) Partition pruning and partition-wise joins on a partitioning key are
important
Q. What are the rules for partitioning a table?
A table can be partitioned if:– It is not part of a cluster– It does not contain LONG or LONG RAW datatypes
Q. What is a global partitioned index?
In a global partitioned index, the keys in a particular index partition may refer to rows stored in more than one underlying table partition or subpartition. A global index can only be range-partitioned, but it can be defined on any type of partitioned table.
Q. What is a local index?
In a local index, all keys in a particular index partition refer only to rows stored in a single underlying table partition. A local index is created by specifying the LOCAL attribute.
Q. What are CLOB and NCLOB datatypes? (Mascot)
The CLOB and NCLOB datatypes store up to four gigabytes of character data in the database. CLOBs store single-byte character set data and NCLOBs store fixed-width and varying-width multibyte national character set data (NCHAR data).
Q. What is PL/SQL?
PL/SQL is Oracle’s procedural language extension to SQL. PL/SQL enables you to mix SQL statements with procedural constructs. With PL/SQL, you can define and execute PL/SQL program units such as procedures, functions, and packages.
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PL/SQL program units generally are categorized as anonymous blocks and stored procedures.
Q. What is an anonymous block?
An anonymous block is a PL/SQL block that appears within your application and it is not named or stored in the database.
Q. What is a Stored Procedure?
A stored procedure is a PL/SQL block that Oracle stores in the database and can be called by name from an application. When you create a stored procedure, Oracle parses the procedure and stores its parsed representation in the database.
Q. What is a distributed transaction?
A distributed transaction is a transaction that includes one or more statements that update data on two or more distinct nodes of a distributed database.
Q. What are packages? (KPIT Infotech, Pune)
A package is a group of related procedures and functions, together with the cursors and variables they use, stored together in the database for continued use as a unit.
While packages allow the administrator or application developer the ability to organize such routines, they also offer increased functionality (for example, global package variables can be declared and used by any procedure in the package) and performance (for example, all objects of the package are parsed, compiled, and loaded into memory once).
Q. What are procedures and functions? (KPIT Infotech, Pune)
A procedure or function is a schema object that consists of a set of SQL statements and other PL/SQL constructs, grouped together, stored in the database, and executed as a unit to solve a specific problem or perform a set of related tasks. Procedures and functions permit the caller to provide parameters that can be input only, output only, or input and output values.
Q. What is the difference between Procedure and Function?
Procedures and functions are identical except that functions always return a single value to the caller, while procedures do not return values to the caller.
Q. What is a DML and what do they do?
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Data manipulation language (DML) statements query or manipulate data in existing schema objects. They enable you to:
1. Retrieve data from one or more tables or views (SELECT)2. Add new rows of data into a table or view (INSERT)3. Change column values in existing rows of a table or view (UPDATE)4. Remove rows from tables or views (DELETE)5. See the execution plan for a SQL statement (EXPLAIN PLAN)6. Lock a table or view, temporarily limiting other users’ access (LOCK
TABLE)
Q. What is a DDL and what do they do?
Data definition language (DDL) statements define, alter the structure of, and drop schema objects. DDL statements enable you to:
1. Create, alter, and drop schema objects and other database structures, including the database itself and database users (CREATE, ALTER, DROP)
2. Change the names of schema objects (RENAME)3. Delete all the data in schema objects without removing the objects’
structure (TRUNCATE)4. Gather statistics about schema objects, validate object structure, and list
chained rows within objects (ANALYZE)5. Grant and revoke privileges and roles (GRANT, REVOKE)6. Turn auditing options on and off (AUDIT, NOAUDIT)7. Add a comment to the data dictionary (COMMENT)
Q. What are shared sql’s?
Oracle automatically notices when applications send identical SQL statements to the database. The SQL area used to process the first occurrence of the statement is shared—that is, used for processing subsequent occurrences of that same statement. Therefore, only one shared SQL area exists for a unique statement. Since shared SQL areas are shared memory areas, any Oracle process can use a shared SQL area. The sharing of SQL areas reduces memory usage on the database server, thereby increasing system throughput.
Q. What are triggers?
Oracle allows to define procedures called triggers that execute implicitly when an INSERT, UPDATE, or DELETE statement is issued against the associated table or, in some cases, against a view, or when database system actions occur. These procedures can be written in PL/SQL or Java and stored in the database, or they can be written as C callouts.
Q. What is Cost-based Optimization?
Using the cost-based approach, the optimizer determines which execution plan is most efficient by considering available access paths and factoring in information based on statistics for the schema objects (tables or indexes) accessed by the SQL statement.
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Q. What is Rule-Based Optimization?
Using the rule-based approach, the optimizer chooses an execution plan based on the access paths available and the ranks of these access paths.
Q. What is meant by degree of parallelism?
The number of parallel execution servers associated with a single operation is known as the degree of parallelism.
Q. What is meant by data consistency?
Data consistency means that each user sees a consistent view of the data, including visible changes made by the user’s own transactions and transactions of other users.
Q. What are Locks?Locks are mechanisms that prevent destructive interaction between transactions accessing the same resource—either user objects such as tables and rows or system objects not visible to users, such as shared data structures in memory and data dictionary rows.
Q. What are the locking modes used in Oracle?Oracle uses two modes of locking in a multiuser database:
Exclusive lock mode: Prevents the associates resource from being shared. This lock mode is obtained to modify data. The first transaction to lock a resource exclusively is the only transaction that can alter the resource until the exclusive lock is released.
Share lock mode: Allows the associated resource to be shared, depending on the operations involved. Multiple users reading data can share the data, holding share locks to prevent concurrent access by a writer (who needs an exclusive lock). Several transactions can acquire share locks on the same resource.
Q. What is a deadlock?A deadlock can occur when two or more users are waiting for data locked by each other.
Q. How can you avoid deadlocks?Multitable deadlocks can usually be avoided if transactions accessing the same tables lock those tables in the same order, either through implicit or explicit locks. For example, all application developers might follow the rule that when both a master and detail table are updated, the master table is locked first and then the detail table. If such rules are properly designed and then followed in all applications, deadlocks are very unlikely to occur.
Q. What is redo log?
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The redo log, present for every Oracle database, records all changes made in an Oracle database. The redo log of a database consists of at least two redo log files that are separate from the datafiles (which actually store a database’s data). As part of database recovery from an instance or media failure, Oracle applies the appropriate changes in the database’s redo log to the datafiles, which updates database data to the instant that the failure occurred.A database’s redo log can consist of two parts: the online redo log and the archived redo log.
Q. What are Rollback Segments?Rollback segments are used for a number of functions in the operation of an Oracle database. In general, the rollback segments of a database store the old values of data changed by ongoing transactions for uncommitted transactions. Among other things, the information in a rollback segment is used during database recovery to undo any uncommitted changes applied from the redo log to the datafiles. Therefore, if database recovery is necessary, then the data is in a consistent state after the rollback segments are used to remove all uncommitted data from the datafiles.
Q. What is SGA?The System Global Area (SGA) is a shared memory region that contains data and control information for one Oracle instance. An SGA and the Oracle background processes constitute an Oracle instance. Oracle allocates the system global area when an instance starts and deallocates it when the instance shuts down. Each instance has its own system global area.
Users currently connected to an Oracle server share the data in the system global area. For optimal performance, the entire system global area should be as large as possible (while still fitting in real memory) to store as much data in memory as possible and minimize disk I/O.
The information stored within the system global area is divided into several types of memory structures, including the database buffers, redo log buffer, and the shared pool. These areas have fixed sizes and are created during instance startup.
Q. What is PCTFREE?The PCTFREE parameter sets the minimum percentage of a data block to be reserved as free space for possible updates to rows that already exist in that block.
Q. What is PCTUSED?The PCTUSED parameter sets the minimum percentage of a block that can be used for row data plus overhead before new rows will be added to the block. After a data block is filled to the limit determined by PCTFREE, Oracle considers the block unavailable for the insertion of new rows until the percentage of that block falls below the parameter PCTUSED. Until this value is achieved, Oracle uses the free space of the data block only for updates to rows already contained in the data block.
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Notes:Nulls are stored in the database if they fall between columns with data values. In these cases they require one byte to store the length of the column (zero). Trailing nulls in a row require no storage because a new row header signals that the remaining columns in the previous row are null. For example, if the last three columns of a table are null, no information is stored for those columns. In tables with many columns, the columns more likely to contain nulls should be defined last to conserve disk space.
Two rows can both contain all nulls without violating a unique index.
NULL values in indexes are considered to be distinct except when all the non-NULL values in two or more rows of an index are identical, in which case the rows are considered to be identical. Therefore, UNIQUE indexes prevent rows containing NULL values from being treated as identical.
Bitmap indexes include rows that have NULL values, unlike most other types of indexes. Indexing of nulls can be useful for some types of SQL statements, such as queries with the aggregate function COUNT.
Bitmap indexes on partitioned tables must be local indexes.
PL/SQL is Oracle’s procedural language extension to SQL. PL/SQL combines theease and flexibility of SQL with the procedural functionality of a structuredprogramming language, such as IF ... THEN, WHILE, and LOOP.When designing a database application, a developer should consider theadvantages of using stored PL/SQL:n Because PL/SQL code can be stored centrally in a database, network trafficbetween applications and the database is reduced, so application and systemperformance increases.n Data access can be controlled by stored PL/SQL code. In this case, the users ofPL/SQL can access data only as intended by the application developer (unlessanother access route is granted).n PL/SQL blocks can be sent by an application to a database, executing complexoperations without excessive network traffic.Even when PL/SQL is not stored in the database, applications can send blocks ofPL/SQL to the database rather than individual SQL statements, thereby againreducing network traffic.The following sections describe the different program units that can be defined andstored centrally in a database.
Committing and Rolling Back TransactionsThe changes made by the SQL statements that constitute a transaction can be either committed or rolled back. After a transaction is committed or rolled back, the next transaction begins with the next SQL statement.
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Committing a transaction makes permanent the changes resulting from all SQL statements in the transaction. The changes made by the SQL statements of a transaction become visible to other user sessions’ transactions that start only after the transaction is committed.Rolling back a transaction retracts any of the changes resulting from the SQL statements in the transaction. After a transaction is rolled back, the affected data is left unchanged as if the SQL statements in the transaction were never executed.
Introduction to the Data DictionaryOne of the most important parts of an Oracle database is its data dictionary, which isa read-only set of tables that provides information about its associated database. Adata dictionary contains:n The definitions of all schema objects in the database (tables, views, indexes,clusters, synonyms, sequences, procedures, functions, packages, triggers,and so on)n How much space has been allocated for, and is currently used by, theschema objectsn Default values for columnsn Integrity constraint informationn The names of Oracle usersn Privileges and roles each user has been grantedn Auditing information, such as who has accessed or updated variousschema objectsn Other general database informationThe data dictionary is structured in tables and views, just like other database data.All the data dictionary tables and views for a given database are stored in thatdatabase’s SYSTEM tablespace.Not only is the data dictionary central to every Oracle database, it is an importanttool for all users, from end users to application designers and databaseadministrators. To access the data dictionary, you use SQL statements. Because thedata dictionary is read-only, you can issue only queries (SELECT statements)against the tables and views of the data dictionary.
Q. What is the function of DUMMY table?
The table named DUAL is a small table in the data dictionary that Oracle and user written programs can reference to guarantee a known result. This table has one column called DUMMY and one row containing the value "X".
Databases, tablespaces, and datafiels are closely related, but they have important differences:
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Databases and tablespaces: An Oracle database consists of one or more logical storage units called tablespaces, which collectively store all of the database’s data.
Tablespaces and datafiles: Each table in an Oracle database consists of one or more files called datafiles, which are physical structures that conform with the operating system in which Oracle is running.
databases and datafiles:A database’s data is collectively stored in the datafiles thatconstitute each tablespace of the database. For example, thesimplest Oracle database would have one tablespace and onedatafile. Another database might have three tablespaces, eachconsisting of two datafiles (for a total of six datafiles).
NullsA null is the absence of a value in a column of a row. Nulls indicate missing,unknown, or inapplicable data. A null should not be used to imply any other value,such as zero. A column allows nulls unless a NOT NULL or PRIMARY KEYintegrity constraint has been defined for the column, in which case no row can beinserted without a value for that column.Nulls are stored in the database if they fall between columns with data values. Inthese cases they require one byte to store the length of the column (zero).Trailing nulls in a row require no storage because a new row header signals that theremaining columns in the previous row are null. For example, if the last threecolumns of a table are null, no information is stored for those columns. In tableswith many columns, the columns more likely to contain nulls should be defined lastto conserve disk space.
Most comparisons between nulls and other values are by definition neither true norfalse, but unknown. To identify nulls in SQL, use the IS NULL predicate. Use theSQL function NVL to convert nulls to non-null values.Nulls are not indexed, except when the cluster key column value is null or the indexis a bitmap index.
What are different types of locks?
Q. Master table and Child table performances and comparisons in Oracle?
Q. What are the different types of Cursors? Explain. (Honeywell)
Q. What are the different types of Deletes?
Q. Can a View be updated?
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Interview Questions from Honeywell
1. What is pragma?2. Can you write commit in triggers?3. Can you call user defined functions in select statements4. Can you call insert/update/delete in select statements. If yes how? If no
what is the other way?5. After update how do you know, how many records got updated6. Select statement does not retrieve any records. What exception is raised?
Interview Questions from Shreesoft
1. How many columns can a PLSQL table have
Interview Questions from mascot1. What is Load balancing & what u have used to do this? (SQL Loader )2. What r Routers?
PL/SQL
1. What are different types of joins?2. Difference between Packages and Procedures3. Difference between Function and Procedures4. How many types of triggers are there? When do you use Triggers5. Can you write DDL statements in Triggers? (No)6. What is Hint?7. How do you tune a SQL query?
Interview Questions from KPIT Infotech, Pune
1. Package body2. What is molar query?3. What is row level security
General:Why ORACLE is the best database for DatawarehousingFor data loading in Oracle, what are conventional loading and direct-path loading ?7. If you use oracle SQL*Loader, how do you transform data with it during loading ? Example.Three ways SQL*Loader could doad data, what are those three types ?What are the contents of "bad files" and "discard files" when using SQL*Loader ?How do you use commit frequencies ? how does it affect loading performance ?
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What are the other factors of the database on which the loading performance depend ?* WHAT IS PARALLELISM ?* WHAT IS A PARALLEL QUERY ?* WHAT ARE DIFFERENT WAYS OF LOADING DATA TO DATAWAREHOUSE USING ORACLE?* WHAT IS TABLE PARTITIONING? HOW IT IS USEFUL TO WAREHOUSE DATABASE?* WHAT ARE DIFFERENT TYPES OF PARTITIONING IN ORACLE?* WHAT IS A MATERIALIZED VIEW? HOW IT IS DIFFERENT FROM NORMAL AND INLINE VIEWS?* WHAT IS INDEXING? WHAT ARE DIFFERENT TYPES OF INDEXES SUPPORTED BY ORACLE?* WHAT ARE DIFFERENT STORAGE OPTIONS SUPPORTED BY ORACLE?* WHAT IS QUERY OPTIMIZER? WHAT ARE DIFFERENT TYPES OF OPTIMIZERS SUPPORTED BY ORACLE?* EXPLAIN ROLLUP,CUBE,RANK AND DENSE_RANK FUNCTIONS OF ORACLE 8i.
The advantages of using bitmap indexes are greatest for low cardinality columns: that is, columns in which the number of distinct values is small compared to the number of rows in the table. A gender column, which only has two distinct values (male and female), is ideal for a bitmap index. However, data warehouse administrators will also choose to build bitmap indexes on columns with much higher cardinalities.
Local vs global: A B-tree index on a partitioned table can be local or global. Global indexes must befully rebuilt after a direct load, which can be very costly when loading a relativelysmall number of rows into a large table. For this reason, it is strongly recommendedthat indexes on partitioned tables should be defined as local indexes unless there isa well-justified performance requirement for a global index. Bitmap indexes onpartitioned tables are always local.
Why Constraints are Useful in a Data WarehouseConstraints provide a mechanism for ensuring that data conforms to guidelinesspecified by the database administrator. The most common types of constraintsinclude unique constraints (ensuring that a given column is unique), not-nullconstraints, and foreign-key constraints (which ensure that two keys share aprimary key-foreign key relationship).
Materialized Views for Data WarehousesIn data warehouses, materialized views can be used to precompute and storeaggregated data such as the sum of sales. Materialized views in these environmentsare typically referred to as summaries, because they store summarized data. They
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can also be used to precompute joins with or without aggregations. A materializedview eliminates the overhead associated with expensive joins or aggregations for alarge or important class of queries.
The Need for Materialized ViewsMaterialized views are used in data warehouses to increase the speed of queries onvery large databases. Queries to large databases often involve joins between tablesor aggregations such as SUM, or both. These operations are very expensive in termsof time and processing power.
How does MV’s work?The query optimizer can use materialized views byautomatically recognizing when an existing materialized view can and should beused to satisfy a request. It then transparently rewrites the request to use thematerialized view. Queries are then directed to the materialized view and not to theunderlying detail tables. In general, rewriting queries to use materialized viewsrather than detail tables results in a significant performance gain.
If a materialized view is to be used by query rewrite, it must be stored in the samedatabase as its fact or detail tables. A materialized view can be partitioned, and youcan define a materialized view on a partitioned table and one or more indexes onthe materialized view.
The types of materialized views are:n Materialized Views with Joins and Aggregatesn Single-Table Aggregate Materialized Viewsn Materialized Views Containing Only Joins
Some Useful system tables:user_tab_partitionsuser_tab_columns
Transact-SQL Optimization Tips Index Optimization tips T-SQL Queries Data Types Index Joins Lock
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Stored Procedure Trigger View Transaction Other XML Tools Permission Administration
Transact-SQL Optimization Tips Use views and stored procedures instead of heavy-duty queries.
This can reduce network traffic, because your client will send to server only stored procedure or view name (perhaps with some parameters) instead of large heavy-duty queries text. This can be used to facilitate permission management also, because you can restrict user access to table columns they should not see.
Try to use constraints instead of triggers, whenever possible.Constraints are much more efficient than triggers and can boost performance. So, you should use constraints instead of triggers, whenever possible.
Use table variables instead of temporary tables.Table variables require less locking and logging resources than temporary tables, so table variables should be used whenever possible. The table variables are available in SQL Server 2000 only.
Try to use UNION ALL statement instead of UNION, whenever possible.The UNION ALL statement is much faster than UNION, because UNION ALL statement does not look for duplicate rows, and UNION statement does look for duplicate rows, whether or not they exist.
Try to avoid using the DISTINCT clause, whenever possible.Because using the DISTINCT clause will result in some performance degradation, you should use this clause only when it is necessary.
Try to avoid using SQL Server cursors, whenever possible.SQL Server cursors can result in some performance degradation in comparison with select statements. Try to use correlated sub-query or derived tables, if you need to perform row-by-row operations.
Try to avoid the HAVING clause, whenever possible.The HAVING clause is used to restrict the result set returned by the GROUP BY clause. When you use GROUP BY with the HAVING clause, the GROUP BY clause divides the rows into sets of grouped rows and aggregates their values, and then the HAVING clause eliminates undesired aggregated groups. In many cases, you can write your select statement so, that it will contain only WHERE and GROUP BY clauses without HAVING clause. This can improve the performance of your query.
If you need to return the total table's row count, you can use alternative way instead of SELECT COUNT(*) statement.Because SELECT COUNT(*) statement make a full table scan to return the total table's row count, it can take very many time for the large table. There is another way to determine the total row count in a table. You can
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use sysindexes system table, in this case. There is ROWS column in the sysindexes table. This column contains the total row count for each table in your database. So, you can use the following select statement instead of SELECT COUNT(*): SELECT rows FROM sysindexes WHERE id = OBJECT_ID('table_name') AND indid < 2 So, you can improve the speed of such queries in several times.
Include SET NOCOUNT ON statement into your stored procedures to stop the message indicating the number of rows affected by a T-SQL statement.This can reduce network traffic, because your client will not receive the message indicating the number of rows affected by a T-SQL statement.
Try to restrict the queries result set by using the WHERE clause.This can results in good performance benefits, because SQL Server will return to client only particular rows, not all rows from the table(s). This can reduce network traffic and boost the overall performance of the query.
Use the select statements with TOP keyword or the SET ROWCOUNT statement, if you need to return only the first n rows.This can improve performance of your queries, because the smaller result set will be returned. This can also reduce the traffic between the server and the clients.
Try to restrict the queries result set by returning only the particular columns from the table, not all table's columns.This can results in good performance benefits, because SQL Server will return to client only particular columns, not all table's columns. This can reduce network traffic and boost the overall performance of the query.
1.Indexes2.avoid more number of triggers on the table3.unnecessary complicated joins4.correct use of Group by clause with the select list5.in worst cases Denormalization
Index Optimization tips
Every index increases the time in takes to perform INSERTS, UPDATES and DELETES, so the number of indexes should not be very much. Try to use maximum 4-5 indexes on one table, not more. If you have read-only table, then the number of indexes may be increased.
Keep your indexes as narrow as possible. This reduces the size of the index and reduces the number of reads required to read the index.
Try to create indexes on columns that have integer values rather than character values.
If you create a composite (multi-column) index, the order of the columns in the key are very important. Try to order the columns in the key as to enhance selectivity, with the most selective columns to the leftmost of the key.
If you want to join several tables, try to create surrogate integer keys for this purpose and create indexes on their columns.
Create surrogate integer primary key (identity for example) if your table will not have many insert operations.
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Clustered indexes are more preferable than nonclustered, if you need to select by a range of values or you need to sort results set with GROUP BY or ORDER BY.
If your application will be performing the same query over and over on the same table, consider creating a covering index on the table.
You can use the SQL Server Profiler Create Trace Wizard with "Identify Scans of Large Tables" trace to determine which tables in your database may need indexes. This trace will show which tables are being scanned by queries instead of using an index.
You can use sp_MSforeachtable undocumented stored procedure to rebuild all indexes in your database. Try to schedule it to execute during CPU idle time and slow production periods.sp_MSforeachtable @command1="print '?' DBCC DBREINDEX ('?')"
T-SQL Queries 1. 2 tables
Employee
Phone
empidempnamesalarymgrid
empidphnumber
2. Select all employees who doesn't have phone?SELECT empnameFROM EmployeeWHERE (empid NOT IN(SELECT DISTINCT empidFROM phone))
3. Select the employee names who is having more than one phone numbers.SELECT empnameFROM employeeWHERE (empid IN(SELECT empidFROM phoneGROUP BY empidHAVING COUNT(empid) > 1))
4. Select the details of 3 max salaried employees from employee table.SELECT TOP 3 empid, salaryFROM employeeORDER BY salary DESC
5. Display all managers from the table. (manager id is same as emp id)SELECT empnameFROM employeeWHERE (empid IN(SELECT DISTINCT mgridFROM employee))
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6. Write a Select statement to list the Employee Name, Manager Name under a particular manager?SELECT e1.empname AS EmpName, e2.empname AS ManagerNameFROM Employee e1 INNER JOINEmployee e2 ON e1.mgrid = e2.empidORDER BY e2.mgrid
7. 2 tables emp and phone.emp fields are - empid, namePh fields are - empid, ph (office, mobile, home). Select all employees who doesn't have any ph nos.SELECT *FROM employee LEFT OUTER JOINphone ON employee.empid = phone.empidWHERE (phone.office IS NULL OR phone.office = ' ')AND (phone.mobile IS NULL OR phone.mobile = ' ')AND (phone.home IS NULL OR phone.home = ' ')
8. Find employee who is living in more than one city. Two Tables:
Emp City
EmpidempNameSalary
EmpidCity
9. SELECT empname, fname, lnameFROM employeeWHERE (empid IN(SELECT empidFROM cityGROUP BY empidHAVING COUNT(empid) > 1))
10.Find all employees who is living in the same city. (table is same as above)SELECT fnameFROM employeeWHERE (empid IN(SELECT empidFROM city aWHERE city IN(SELECT cityFROM city bGROUP BY cityHAVING COUNT(city) > 1)))
11.There is a table named MovieTable with three columns - moviename, person and role. Write a query which gets the movie details where Mr. Amitabh and Mr. Vinod acted and their role is actor.SELECT DISTINCT m1.movienameFROM MovieTable m1 INNER JOINMovieTable m2 ON m1.moviename = m2.movienameWHERE (m1.person = 'amitabh' AND m2.person = 'vinod' ORm2.person = 'amitabh' AND m1.person = 'vinod') AND (m1.role = 'actor')
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AND (m2.role = 'actor')ORDER BY m1.moviename
12.There are two employee tables named emp1 and emp2. Both contains same structure (salary details). But Emp2 salary details are incorrect and emp1 salary details are correct. So, write a query which corrects salary details of the table emp2update a set a.sal=b.sal from emp1 a, emp2 b where a.empid=b.empid
13.Given a Table named “Students” which contains studentid, subjectid and marks. Where there are 10 subjects and 50 students. Write a Query to find out the Maximum marks obtained in each subject.
14. In this same tables now write a SQL Query to get the studentid also to combine with previous results.
15.Three tables – student , course, marks – how do go at finding name of the students who got max marks in the diff courses.SELECT student.name, course.name AS coursename, marks.sid, marks.markFROM marks INNER JOINstudent ON marks.sid = student.sid INNER JOINcourse ON marks.cid = course.cidWHERE (marks.mark =(SELECT MAX(Mark)FROM Marks MaxMarkWHERE MaxMark.cID = Marks.cID))
16.There is a table day_temp which has three columns dayid, day and temperature. How do I write a query to get the difference of temperature among each other for seven days of a week?SELECT a.dayid, a.dday, a.tempe, a.tempe - b.tempe AS DifferenceFROM day_temp a INNER JOINday_temp b ON a.dayid = b.dayid + 1ORSelect a.day, a.degree-b.degree from temperature a, temperature b where a.id=b.id+1
17.There is a table which contains the names like this. a1, a2, a3, a3, a4, a1, a1, a2 and their salaries. Write a query to get grand total salary, and total salaries of individual employees in one query.SELECT empid, SUM(salary) AS salaryFROM employeeGROUP BY empid WITH ROLLUPORDER BY empid
18.How to know how many tables contains empno as a column in a database?SELECT COUNT(*) AS CounterFROM syscolumnsWHERE (name = 'empno')
19.Find duplicate rows in a table? OR I have a table with one column which has many records which are not distinct. I need to find the distinct values from that column and number of times it’s repeated.SELECT sid, mark, COUNT(*) AS CounterFROM marks
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GROUP BY sid, markHAVING (COUNT(*) > 1)
20.How to delete the rows which are duplicate (don’t delete both duplicate records).SET ROWCOUNT 1DELETE yourtableFROM yourtable aWHERE (SELECT COUNT(*) FROM yourtable b WHERE b.name1 = a.name1 AND b.age1 = a.age1) > 1WHILE @@rowcount > 0 DELETE yourtable FROM yourtable a WHERE (SELECT COUNT(*) FROM yourtable b WHERE b.name1 = a.name1 AND b.age1 = a.age1) > 1SET ROWCOUNT 0
21.How to find 6th highest salarySELECT TOP 1 salaryFROM (SELECT DISTINCT TOP 6 salaryFROM employeeORDER BY salary DESC) aORDER BY salary
22.Find top salary among two tablesSELECT TOP 1 salFROM (SELECT MAX(sal) AS salFROM sal1UNIONSELECT MAX(sal) AS salFROM sal2) aORDER BY sal DESC
23.Write a query to convert all the letters in a word to upper caseSELECT UPPER('test')
24.Write a query to round up the values of a number. For example even if the user enters 7.1 it should be rounded up to 8.SELECT CEILING (7.1)
25.Write a SQL Query to find first day of month?SELECT DATENAME(dw, DATEADD(dd, - DATEPART(dd, GETDATE()) + 1, GETDATE())) AS FirstDay
Datepart Abbreviations
year yy, yyyy
quarter qq, q
month mm, m
dayofyear dy, y
day dd, d
week wk, ww
weekday dw
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hour hh
minute mi, n
second ss, s
millisecond ms
26.Table A contains column1 which is primary key and has 2 values (1, 2) and Table B contains column1 which is primary key and has 2 values (2, 3). Write a query which returns the values that are not common for the tables and the query should return one column with 2 records.SELECT tbla.aFROM tbla, tblbWHERE tbla.a <>(SELECT tblb.aFROM tbla, tblbWHERE tbla.a = tblb.a)UNIONSELECT tblb.aFROM tbla, tblbWHERE tblb.a <>(SELECT tbla.aFROM tbla, tblbWHERE tbla.a = tblb.a)
OR (better approach)
SELECT aFROM tblaWHERE a NOT IN(SELECT aFROM tblb)UNION ALLSELECT aFROM tblbWHERE a NOT IN(SELECT aFROM tbla)
27.There are 3 tables Titles, Authors and Title-Authors (check PUBS db). Write the query to get the author name and the number of books written by that author, the result should start from the author who has written the maximum number of books and end with the author who has written the minimum number of books.SELECT authors.au_lname, COUNT(*) AS BooksCountFROM authors INNER JOINtitleauthor ON authors.au_id = titleauthor.au_id INNER JOINtitles ON titles.title_id = titleauthor.title_idGROUP BY authors.au_lnameORDER BY BooksCount DESC
28.UPDATE emp_master
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SET emp_sal = CASEWHEN emp_sal > 0 AND emp_sal <= 20000 THEN (emp_sal * 1.01) WHEN emp_sal > 20000 THEN (emp_sal * 1.02) END
29.List all products with total quantity ordered, if quantity ordered is null show it as 0.SELECT name, CASE WHEN SUM(qty) IS NULL THEN 0 WHEN SUM(qty) > 0 THEN SUM(qty) END AS totFROM [order] RIGHT OUTER JOINproduct ON [order].prodid = product.prodidGROUP BY nameResult:coke 60mirinda 0pepsi 10
30.ANY, SOME, or ALL?ALL means greater than every value--in other words, greater than the maximum value. For example, >ALL (1, 2, 3) means greater than 3.ANY means greater than at least one value, that is, greater than the minimum. So >ANY (1, 2, 3) means greater than 1. SOME is an SQL-92 standard equivalent for ANY.
31. IN & = (difference in correlated sub query)
INDEX 32.What is Index? It’s purpose?
Indexes in databases are similar to indexes in books. In a database, an index allows the database program to find data in a table without scanning the entire table. An index in a database is a list of values in a table with the storage locations of rows in the table that contain each value. Indexes can be created on either a single column or a combination of columns in a table and are implemented in the form of B-trees. An index contains an entry with one or more columns (the search key) from each row in a table. A B-tree is sorted on the search key, and can be searched efficiently on any leading subset of the search key. For example, an index on columns A, B, C can be searched efficiently on A, on A, B, and A, B, C.
33.Explain about Clustered and non clustered index? How to choose between a Clustered Index and a Non-Clustered Index?There are clustered and nonclustered indexes. A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages. A nonclustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf nodes of a nonclustered index does not consist of the data pages. Instead, the leaf nodes contain index rows.Consider using a clustered index for:
o Columns that contain a large number of distinct values.
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o Queries that return a range of values using operators such as BETWEEN, >, >=, <, and <=.
o Columns that are accessed sequentially. o Queries that return large result sets.
Non-clustered indexes have the same B-tree structure as clustered indexes, with two significant differences:
o The data rows are not sorted and stored in order based on their non-clustered keys.
o The leaf layer of a non-clustered index does not consist of the data pages. Instead, the leaf nodes contain index rows. Each index row contains the non-clustered key value and one or more row locators that point to the data row (or rows if the index is not unique) having the key value.
o Per table only 249 non clustered indexes. 34.Disadvantage of index?
Every index increases the time in takes to perform INSERTS, UPDATES and DELETES, so the number of indexes should not be very much.
35.Given a scenario that I have a 10 Clustered Index in a Table to all their 10 Columns. What are the advantages and disadvantages?A: Only 1 clustered index is possible.
36.How can I enforce to use particular index?You can use index hint (index=<index_name>) after the table name.SELECT au_lname FROM authors (index=aunmind)
37.What is Index Tuning?One of the hardest tasks facing database administrators is the selection of appropriate columns for non-clustered indexes. You should consider creating non-clustered indexes on any columns that are frequently referenced in the WHERE clauses of SQL statements. Other good candidates are columns referenced by JOIN and GROUP BY operations.You may wish to also consider creating non-clustered indexes that cover all of the columns used by certain frequently issued queries. These queries are referred to as “covered queries” and experience excellent performance gains.Index Tuning is the process of finding appropriate column for non-clustered indexes.SQL Server provides a wonderful facility known as the Index Tuning Wizard which greatly enhances the index selection process.
38.Difference between Index defrag and Index rebuild?When you create an index in the database, the index information used by queries is stored in index pages. The sequential index pages are chained together by pointers from one page to the next. When changes are made to the data that affect the index, the information in the index can become scattered in the database. Rebuilding an index reorganizes the storage of the index data (and table data in the case of a clustered index) to remove fragmentation. This can improve disk performance by reducing the number of page reads required to obtain the requested dataDBCC INDEXDEFRAG - Defragments clustered and secondary indexes of the specified table or view.**
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39.What is sorting and what is the difference between sorting & clustered indexes?The ORDER BY clause sorts query results by one or more columns up to 8,060 bytes. This will happen by the time when we retrieve data from database. Clustered indexes physically sorting data, while inserting/updating the table.
40.What are statistics, under what circumstances they go out of date, how do you update them?Statistics determine the selectivity of the indexes. If an indexed column has unique values then the selectivity of that index is more, as opposed to an index with non-unique values. Query optimizer uses these indexes in determining whether to choose an index or not while executing a query.Some situations under which you should update statistics:1) If there is significant change in the key values in the index2) If a large amount of data in an indexed column has been added, changed, or removed (that is, if the distribution of key values has changed), or the table has been truncated using the TRUNCATE TABLE statement and then repopulated3) Database is upgraded from a previous version
41.What is fillfactor? What is the use of it ? What happens when we ignore it? When you should use low fill factor?When you create a clustered index, the data in the table is stored in the data pages of the database according to the order of the values in the indexed columns. When new rows of data are inserted into the table or the values in the indexed columns are changed, Microsoft® SQL Server™ 2000 may have to reorganize the storage of the data in the table to make room for the new row and maintain the ordered storage of the data. This also applies to nonclustered indexes. When data is added or changed, SQL Server may have to reorganize the storage of the data in the nonclustered index pages. When a new row is added to a full index page, SQL Server moves approximately half the rows to a new page to make room for the new row. This reorganization is known as a page split. Page splitting can impair performance and fragment the storage of the data in a table.When creating an index, you can specify a fill factor to leave extra gaps and reserve a percentage of free space on each leaf level page of the index to accommodate future expansion in the storage of the table's data and reduce the potential for page splits. The fill factor value is a percentage from 0 to 100 that specifies how much to fill the data pages after the index is created. A value of 100 means the pages will be full and will take the least amount of storage space. This setting should be used only when there will be no changes to the data, for example, on a read-only table. A lower value leaves more empty space on the data pages, which reduces the need to split data pages as indexes grow but requires more storage space. This setting is more appropriate when there will be changes to the data in the table.
DATA TYPES 42.What are the data types in SQL
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bigint Binary bit char cursor
datetime Decimal float image int
money Nchar ntext nvarchar real
smalldatetime Smallint smallmoney text timestamp
tinyint Varbinary Varchar uniqueidentifier
43.Difference between char and nvarchar / char and varchar data-type?char[(n)] - Fixed-length non-Unicode character data with length of n bytes. n must be a value from 1 through 8,000. Storage size is n bytes. The SQL-92 synonym for char is character.nvarchar(n) - Variable-length Unicode character data of n characters. n must be a value from 1 through 4,000. Storage size, in bytes, is two times the number of characters entered. The data entered can be 0 characters in length. The SQL-92 synonyms for nvarchar are national char varying and national character varying. varchar[(n)] - Variable-length non-Unicode character data with length of n bytes. n must be a value from 1 through 8,000. Storage size is the actual length in bytes of the data entered, not n bytes. The data entered can be 0 characters in length. The SQL-92 synonyms for varchar are char varying or character varying.
44.GUID datasize?128bit
45.How GUID becoming unique across machines?To ensure uniqueness across machines, the ID of the network card is used (among others) to compute the number.
46.What is the difference between text and image data type?Text and image. Use text for character data if you need to store more than 255 characters in SQL Server 6.5, or more than 8000 in SQL Server 7.0. Use image for binary large objects (BLOBs) such as digital images. With text and image data types, the data is not stored in the row, so the limit of the page size does not apply.All that is stored in the row is a pointer to the database pages that contain the data.Individual text, ntext, and image values can be a maximum of 2-GB, which is too long to store in a single data row.
JOINS 47.What are joins?
Sometimes we have to select data from two or more tables to make our result complete. We have to perform a join.
48.How many types of Joins?Joins can be categorized as:
Inner joins (the typical join operation, which uses some comparison operator like = or <>). These include equi-joins and natural joins. Inner joins use a comparison operator to match rows from two tables based on the values in common columns from each table. For example, retrieving all rows where the student identification number is the same in both the students and courses tables.
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Outer joins. Outer joins can be a left, a right, or full outer join. Outer joins are specified with one of the following sets of keywords when they are specified in the FROM clause:
LEFT JOIN or LEFT OUTER JOIN -The result set of a left outer join includes all the rows from the left table specified in the LEFT OUTER clause, not just the ones in which the joined columns match. When a row in the left table has no matching rows in the right table, the associated result set row contains null values for all select list columns coming from the right table.
RIGHT JOIN or RIGHT OUTER JOIN - A right outer join is the reverse of a left outer join. All rows from the right table are returned. Null values are returned for the left table any time a right table row has no matching row in the left table.
FULL JOIN or FULL OUTER JOIN - A full outer join returns all rows in both the left and right tables. Any time a row has no match in the other table, the select list columns from the other table contain null values. When there is a match between the tables, the entire result set row contains data values from the base tables.
Cross joins - Cross joins return all rows from the left table, each row from the left table is combined with all rows from the right table. Cross joins are also called Cartesian products. (A Cartesian join will get you a Cartesian product. A Cartesian join is when you join every row of one table to every row of another table. You can also get one by joining every row of a table to every row of itself.)
2. What is self join?A table can be joined to itself in a self-join.
3. What are the differences between UNION and JOINS?A join selects columns from 2 or more tables. A union selects rows.
4. Can I improve performance by using the ANSI-style joins instead of the old-style joins?Code Example 1:select o.name, i.namefrom sysobjects o, sysindexes iwhere o.id = i.idCode Example 2:select o.name, i.namefrom sysobjects o inner join sysindexes ion o.id = i.idYou will not get any performance gain by switching to the ANSI-style JOIN syntax.Using the ANSI-JOIN syntax gives you an important advantage: Because the join logic is cleanly separated from the filtering criteria, you can understand the query logic more quickly.The SQL Server old-style JOIN executes the filtering conditions before executing the joins, whereas the ANSI-style JOIN reverses this procedure (join logic precedes filtering).Perhaps the most compelling argument for switching to the ANSI-style
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JOIN is that Microsoft has explicitly stated that SQL Server will not support the old-style OUTER JOIN syntax indefinitely. Another important consideration is that the ANSI-style JOIN supports query constructions that the old-style JOIN syntax does not support.
5. What is derived table?Derived tables are SELECT statements in the FROM clause referred to by an alias or a user-specified name. The result set of the SELECT in the FROM clause forms a table used by the outer SELECT statement. For example, this SELECT uses a derived table to find if any store carries all book titles in the pubs database: SELECT ST.stor_id, ST.stor_nameFROM stores AS ST, (SELECT stor_id, COUNT(DISTINCT title_id) AS title_count FROM sales GROUP BY stor_id ) AS SAWHERE ST.stor_id = SA.stor_idAND SA.title_count = (SELECT COUNT(*) FROM titles)
STORED PROCEDURE 6. What is Stored procedure?
A stored procedure is a set of Structured Query Language (SQL) statements that you assign a name to and store in a database in compiled form so that you can share it between a number of programs.
They allow modular programming. They allow faster execution. They can reduce network traffic. They can be used as a security mechanism.
7. What are the different types of Storage Procedure?
a. Temporary Stored Procedures - SQL Server supports two types of temporary procedures: local and global. A local temporary procedure is visible only to the connection that created it. A global temporary procedure is available to all connections. Local temporary procedures are automatically dropped at the end of the current session. Global temporary procedures are dropped at the end of the last session using the procedure. Usually, this is when the session that created the procedure ends. Temporary procedures named with # and ## can be created by any user.
b. System stored procedures are created and stored in the master database and have the sp_ prefix.(or xp_) System stored procedures can be executed from any database without having to qualify the stored procedure name fully using the database name master. (If any user-created stored procedure has the same name as a system stored procedure, the user-created stored procedure will never be executed.)
c. Automatically Executing Stored Procedures - One or more stored procedures can execute automatically when SQL Server starts. The stored procedures must be created by the system administrator and
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executed under the sysadmin fixed server role as a background process. The procedure(s) cannot have any input parameters.
d. User stored procedure 2. How do I mark the stored procedure to automatic execution?
You can use the sp_procoption system stored procedure to mark the stored procedure to automatic execution when the SQL Server will start. Only objects in the master database owned by dbo can have the startup setting changed and this option is restricted to objects that have no parameters.USE masterEXEC sp_procoption 'indRebuild', 'startup', 'true')
3. How can you optimize a stored procedure? 4. How will know whether the SQL statements are executed?
When used in a stored procedure, the RETURN statement can specify an integer value to return to the calling application, batch, or procedure. If no value is specified on RETURN, a stored procedure returns the value 0. The stored procedures return a value of 0 when no errors were encountered. Any nonzero value indicates an error occurred.
5. Why one should not prefix user stored procedures with sp_?It is strongly recommended that you do not create any stored procedures using sp_ as a prefix. SQL Server always looks for a stored procedure beginning with sp_ in this order:
1. The stored procedure in the master database. 2. The stored procedure based on any qualifiers provided (database
name or owner). 3. The stored procedure using dbo as the owner, if one is not
specified.
Therefore, although the user-created stored procedure prefixed with sp_ may exist in the current database, the master database is always checked first, even if the stored procedure is qualified with the database name.
2. What can cause a Stored procedure execution plan to become invalidated and/or fall out of cache?
1. Server restart 2. Plan is aged out due to low use 3. DBCC FREEPROCCACHE (sometime desired to force it)
3. When do one need to recompile stored procedure?if a new index is added from which the stored procedure might benefit, optimization does not automatically happen (until the next time the stored procedure is run after SQL Server is restarted).
4. SQL Server provides three ways to recompile a stored procedure:
The sp_recompile system stored procedure forces a recompile of a stored procedure the next time it is run.
Creating a stored procedure that specifies the WITH RECOMPILE option in its definition indicates that SQL Server does not cache a plan for this stored procedure; the stored procedure is recompiled
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each time it is executed. Use the WITH RECOMPILE option when stored procedures take parameters whose values differ widely between executions of the stored procedure, resulting in different execution plans to be created each time. Use of this option is uncommon, and causes the stored procedure to execute more slowly because the stored procedure must be recompiled each time it is executed.
You can force the stored procedure to be recompiled by specifying the WITH RECOMPILE option when you execute the stored procedure. Use this option only if the parameter you are supplying is atypical or if the data has significantly changed since the stored procedure was created.
8. How to find out which stored procedure is recompiling? How to stop stored procedures from recompiling?
9. I have Two Stored Procedures SP1 and SP2 as given below. How the Transaction works, whether SP2 Transaction succeeds or fails?CREATE PROCEDURE SP1 ASBEGIN TRANINSERT INTO MARKS (SID,MARK,CID) VALUES (5,6,3)EXEC SP2ROLLBACKGO
CREATE PROCEDURE SP2 ASBEGIN TRANINSERT INTO MARKS (SID,MARK,CID) VALUES (100,100,103)commit tranGOBoth will get roll backed.
10. CREATE PROCEDURE SP1 ASBEGIN TRAN INSERT INTO MARKS (SID,MARK,CID) VALUES (5,6,3) BEGIN TRAN INSERT INTO STUDENT (SID,NAME1) VALUES (1,'SA') commit tranROLLBACK TRANGOBoth will get roll backed.
11. How will you handle Errors in Sql Stored Procedure?INSERT NonFatal VALUES (@Column2)IF @@ERROR <>0 BEGIN PRINT 'Error Occured' END http://www.sqlteam.com/item.asp?ItemID=2463
12. How will you raise an error in sql?RAISERROR - Returns a user-defined error message and sets a system flag to record that an error has occurred. Using RAISERROR, the client can either retrieve an entry from the sysmessages table or build a message dynamically with user-specified severity and state information.
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After the message is defined it is sent back to the client as a server error message.
13. I have a stored procedure likecommit trancreate table a()insert into table b----rollback tranwhat will be the result? Is table created? data will be inserted in table b?
14. What do you do when one procedure is blocking the other?**
15. How you will return XML from Stored Procedure?You use the FOR XML clause of the SELECT statement, and within the FOR XML clause you specify an XML mode: RAW, AUTO, or EXPLICIT.
16. What are the differences between RAW, AUTO and Explicit modes in retrieving data from SQL Server in XML format?**
17. Can a Stored Procedure call itself (recursive). If so then up to what level and can it be control?Stored procedures are nested when one stored procedure calls another. You can nest stored procedures up to 32 levels. The nesting level increases by one when the called stored procedure begins execution and decreases by one when the called stored procedure completes execution. Attempting to exceed the maximum of 32 levels of nesting causes the whole calling stored procedure chain to fail. The current nesting level for the stored procedures in execution is stored in the @@NESTLEVEL function.eg:SET NOCOUNT ONUSE masterIF OBJECT_ID('dbo.sp_calcfactorial') IS NOT NULLDROP PROC dbo.sp_calcfactorialGOCREATE PROC dbo.sp_calcfactorial@base_number int, @factorial int OUTASDECLARE @previous_number intIF (@base_number<2) SET @factorial=1 -- Factorial of 0 or 1=1ELSE BEGINSET @previous_number=@base_number-1EXEC dbo.sp_calcfactorial @previous_number, @factorial OUT -- Recursive callIF (@factorial=-1) RETURN(-1) -- Got an error, returnSET @factorial=@factorial*@base_numberENDRETURN(0)GO
calling proc.
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DECLARE @factorial int EXEC dbo.sp_calcfactorial 4, @factorial OUT SELECT @factorial
18. Nested TriggersTriggers are nested when a trigger performs an action that initiates another trigger, which can initiate another trigger, and so on. Triggers can be nested up to 32 levels, and you can control whether triggers can be nested through the nested triggers server configuration option.
19. What is an extended stored procedure? Can you instantiate a COM object by using T-SQL? An extended stored procedure is a function within a DLL (written in a programming language like C, C++ using Open Data Services (ODS) API) that can be called from T-SQL, just the way we call normal stored procedures using the EXEC statement.
20. Difference between view and stored procedure?Views can have only select statements (create, update, truncate, delete statements are not allowed) Views cannot have “select into”, “Group by” “Having”, ”Order by”
21. What is a Function & what are the different user defined functions?Function is a saved Transact-SQL routine that returns a value. User-defined functions cannot be used to perform a set of actions that modify the global database state. User-defined functions, like system functions, can be invoked from a query. They also can be executed through an EXECUTE statement like stored procedures.
1. Scalar FunctionsFunctions are scalar-valued if the RETURNS clause specified one of the scalar data types
2. Inline Table-valued FunctionsIf the RETURNS clause specifies TABLE with no accompanying column list, the function is an inline function.
3. Multi-statement Table-valued FunctionsIf the RETURNS clause specifies a TABLE type with columns and their data types, the function is a multi-statement table-valued function.
5. What are the difference between a function and a stored procedure?1. Functions can be used in a select statement where as procedures
cannot 2. Procedure takes both input and output parameters but Functions
takes only input parameters 3. Functions cannot return values of type text, ntext, image &
timestamps where as procedures can 4. Functions can be used as user defined datatypes in create table
but procedures cannot ***Eg:-create table <tablename>(name varchar(10),salary getsal(name))Here getsal is a user defined function which returns a salary type, when table is created no storage is allotted for salary type, and getsal function is also not executed, But when we are fetching
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some values from this table, getsal function get’s executed and the return Type is returned as the result set.
6. How to debug a stored procedure?
TRIGGER 7. What is Trigger? What is its use? What are the types of Triggers?
What are the new kinds of triggers in sql 2000?Triggers are a special class of stored procedure defined to execute automatically when an UPDATE, INSERT, or DELETE statement is issued against a table or view. Triggers are powerful tools that sites can use to enforce their business rules automatically when data is modified.The CREATE TRIGGER statement can be defined with the FOR UPDATE, FOR INSERT, or FOR DELETE clauses to target a trigger to a specific class of data modification actions. When FOR UPDATE is specified, the IF UPDATE (column_name) clause can be used to target a trigger to updates affecting a particular column.You can use the FOR clause to specify when a trigger is executed:
AFTER (default) - The trigger executes after the statement that triggered it completes. If the statement fails with an error, such as a constraint violation or syntax error, the trigger is not executed. AFTER triggers cannot be specified for views.
INSTEAD OF -The trigger executes in place of the triggering action. INSTEAD OF triggers can be specified on both tables and views. You can define only one INSTEAD OF trigger for each triggering action (INSERT, UPDATE, and DELETE). INSTEAD OF triggers can be used to perform enhance integrity checks on the data values supplied in INSERT and UPDATE statements. INSTEAD OF triggers also let you specify actions that allow views, which would normally not support updates, to be updatable.An INSTEAD OF trigger can take actions such as:
Ignoring parts of a batch. Not processing a part of a batch and logging the problem
rows. Taking an alternative action if an error condition is
encountered.
In SQL Server 6.5 you could define only 3 triggers per table, one for INSERT, one for UPDATE and one for DELETE. From SQL Server 7.0 onwards, this restriction is gone, and you could create multiple triggers per each action. But in 7.0 there's no way to control the order in which the triggers fire. In SQL Server 2000 you could specify which trigger fires first or fires last using sp_settriggerorder.Till SQL Server 7.0, triggers fire only after the data modification operation happens. So in a way, they are called post triggers. But in SQL Server 2000 you could create pre triggers also.
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22. When should one use "instead of Trigger"? ExampleCREATE TABLE BaseTable(PrimaryKey int IDENTITY(1,1),Color nvarchar(10) NOT NULL,Material nvarchar(10) NOT NULL,ComputedCol AS (Color + Material))GO
--Create a view that contains all columns from the base table.CREATE VIEW InsteadViewAS SELECT PrimaryKey, Color, Material, ComputedColFROM BaseTableGO
--Create an INSTEAD OF INSERT trigger on tthe view.CREATE TRIGGER InsteadTrigger on InsteadViewINSTEAD OF INSERTASBEGIN--Build an INSERT statement ignoring inserrted.PrimaryKey and --inserted.ComputedCol.INSERT INTO BaseTableSELECT Color, MaterialFROM insertedENDGO
-- can insert value to basetable by this insert into basetable(color,material) values ('red','abc')
-- insert into InsteadView(color,material)) values ('red','abc') can't do this.-- It will give error "'PrimaryKey' iin table 'InsteadView' cannot be null."
-- can insert value through table by this<insert into InsteadView values (1,'red','abc',1) --PrimaryKey, ComputedCol wont take values from here
23. Difference between trigger and stored procedure?Trigger will get execute automatically when an UPDATE, INSERT, or DELETE statement is issued against a table or view.We have to call stored procedure manually, or it can execute automatic when the SQL Server starts (You can use the sp_procoption system stored procedure to mark the stored procedure to automatic execution when the SQL Server will start.
24. The following trigger generates an e-mail whenever a new title is added.CREATE TRIGGER reminderON titlesFOR INSERT
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ASEXEC master..xp_sendmail 'MaryM', 'New title, mention in the next report to distributors.'
25. Drawback of trigger? Its alternative solution?Triggers are generally used to implement business rules, auditing. Triggers can also be used to extend the referential integrity checks, but wherever possible, use constraints for this purpose, instead of triggers, as constraints are much faster.
LOCK 26. What are locks?
Microsoft® SQL Server™ 2000 uses locking to ensure transactional integrity and database consistency. Locking prevents users from reading data being changed by other users, and prevents multiple users from changing the same data at the same time. If locking is not used, data within the database may become logically incorrect, and queries executed against that data may produce unexpected results.
27. What are the different types of locks?SQL Server uses these resource lock modes.
Lock modeDescription
Shared (S)Used for operations that do not change or update data (read-only operations), such as a SELECT statement.
Update (U)Used on resources that can be updated. Prevents a common form of deadlock that occurs when multiple sessions are reading, locking, and potentially updating resources later.
Exclusive (X)
Used for data-modification operations, such as INSERT, UPDATE, or DELETE. Ensures that multiple updates cannot be made to the same resource at the same time.
IntentUsed to establish a lock hierarchy. The types of intent locks are: intent shared (IS), intent exclusive (IX), and shared with intent exclusive (SIX).
SchemaUsed when an operation dependent on the schema of a table is executing. The types of schema locks are: schema modification (Sch-M) and schema stability (Sch-S).
Bulk Update (BU)
Used when bulk-copying data into a table and the TABLOCK hint is specified.
28. What is a dead lock? Give a practical sample? How you can minimize the deadlock situation? What is a deadlock and what is a live lock? How will you go about resolving deadlocks?Deadlock is a situation when two processes, each having a lock on one piece of data, attempt to acquire a lock on the other's piece. Each process would wait indefinitely for the other to release the lock, unless one of the user processes is terminated. SQL Server detects deadlocks and terminates one user's process.A livelock is one, where a request for an exclusive lock is repeatedly denied because a series of overlapping shared locks keeps interfering. SQL Server detects the situation after four denials and refuses further
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shared locks. (A livelock also occurs when read transactions monopolize a table or page, forcing a write transaction to wait indefinitely.)
29. What is isolation level?An isolation level determines the degree of isolation of data between concurrent transactions. The default SQL Server isolation level is Read Committed. A lower isolation level increases concurrency, but at the expense of data correctness. Conversely, a higher isolation level ensures that data is correct, but can affect concurrency negatively. The isolation level required by an application determines the locking behavior SQL Server uses.SQL-92 defines the following isolation levels, all of which are supported by SQL Server:
Read uncommitted (the lowest level where transactions are isolated only enough to ensure that physically corrupt data is not read).
Read committed (SQL Server default level). Repeatable read. Serializable (the highest level, where transactions are completely isolated
from one another).
Isolation level Dirty read Nonrepeatable read Phantom
Read uncommitted Yes Yes Yes
Read committed No Yes Yes
Repeatable read No No Yes
Serializable No No No
30. Uncommitted Dependency (Dirty Read) - Uncommitted dependency occurs when a second transaction selects a row that is being updated by another transaction. The second transaction is reading data that has not been committed yet and may be changed by the transaction updating the row. For example, an editor is making changes to an electronic document. During the changes, a second editor takes a copy of the document that includes all the changes made so far, and distributes the document to the intended audience.Inconsistent Analysis (Nonrepeatable Read) Inconsistent analysis occurs when a second transaction accesses the same row several times and reads different data each time. Inconsistent analysis is similar to uncommitted dependency in that another transaction is changing the data that a second transaction is reading. However, in inconsistent analysis, the data read by the second transaction was committed by the transaction that made the change. Also, inconsistent analysis involves multiple reads (two or more) of the same row and each time the information is changed by another transaction; thus, the term nonrepeatable read. For example, an editor reads the same document twice, but between each reading, the writer rewrites the document. When the editor reads the document for the second time, it has changed.Phantom Reads Phantom reads occur when an insert or delete action is performed against a row that belongs to a range of rows being read by a transaction. The transaction's first read of the range of rows shows a row that no longer exists in the second or succeeding read, as a result of a deletion by a different transaction. Similarly, as the result of an insert by a
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different transaction, the transaction's second or succeeding read shows a row that did not exist in the original read. For example, an editor makes changes to a document submitted by a writer, but when the changes are incorporated into the master copy of the document by the production department, they find that new unedited material has been added to the document by the author. This problem could be avoided if no one could add new material to the document until the editor and production department finish working with the original document.
31. nolock? What is the difference between the REPEATABLE READ and SERIALIZE isolation levels?Locking Hints - A range of table-level locking hints can be specified using the SELECT, INSERT, UPDATE, and DELETE statements to direct Microsoft® SQL Server 2000 to the type of locks to be used. Table-level locking hints can be used when a finer control of the types of locks acquired on an object is required. These locking hints override the current transaction isolation level for the session.
Locking hint Description
HOLDLOCK Hold a shared lock until completion of the transaction instead of releasing the lock as soon as the required table, row, or data page is no longer required. HOLDLOCK is equivalent to SERIALIZABLE.
NOLOCK Do not issue shared locks and do not honor exclusive locks. When this option is in effect, it is possible to read an uncommitted transaction or a set of pages that are rolled back in the middle of a read. Dirty reads are possible. Only applies to the SELECT statement.
PAGLOCK Use page locks where a single table lock would usually be taken.
READCOMMITTED Perform a scan with the same locking semantics as a transaction running at the READ COMMITTED isolation level. By default, SQL Server 2000 operates at this isolation level.
READPAST Skip locked rows. This option causes a transaction to skip rows locked by other transactions that would ordinarily appear in the result set, rather than block the transaction waiting for the other transactions to release their locks on these rows. The READPAST lock hint applies only to transactions operating at READ COMMITTED isolation and will read only past row-level locks. Applies only to the SELECT statement.
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READUNCOMMITTED
Equivalent to NOLOCK.
REPEATABLEREAD Perform a scan with the same locking semantics as a transaction running at the REPEATABLE READ isolation level.
ROWLOCK Use row-level locks instead of the coarser-grained page- and table-level locks.
SERIALIZABLE Perform a scan with the same locking semantics as a transaction running at the SERIALIZABLE isolation level. Equivalent to HOLDLOCK.
TABLOCK Use a table lock instead of the finer-grained row- or page-level locks. SQL Server holds this lock until the end of the statement. However, if you also specify HOLDLOCK, the lock is held until the end of the transaction.
TABLOCKX Use an exclusive lock on a table. This lock prevents others from reading or updating the table and is held until the end of the statement or transaction.
UPDLOCK Use update locks instead of shared locks while reading a table, and hold locks until the end of the statement or transaction. UPDLOCK has the advantage of allowing you to read data (without blocking other readers) and update it later with the assurance that the data has not changed since you last read it.
XLOCK Use an exclusive lock that will be held until the end of the transaction on all data processed by the statement. This lock can be specified with either PAGLOCK or TABLOCK, in which case the exclusive lock applies to the appropriate level of granularity.
32. For example, if the transaction isolation level is set to SERIALIZABLE, and the table-level locking hint NOLOCK is used with the SELECT statement, key-range locks typically used to maintain serializable transactions are not taken.USE pubsGOSET TRANSACTION ISOLATION LEVEL SERIALIZABLEGO
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BEGIN TRANSACTIONSELECT au_lname FROM authors WITH (NOLOCK)GO
33. What is escalation of locks?Lock escalation is the process of converting a lot of low level locks (like row locks, page locks) into higher level locks (like table locks). Every lock is a memory structure too many locks would mean, more memory being occupied by locks. To prevent this from happening, SQL Server escalates the many fine-grain locks to fewer coarse-grain locks. Lock escalation threshold was definable in SQL Server 6.5, but from SQL Server 7.0 onwards it's dynamically managed by SQL Server.
VIEW 34. What is View? Use? Syntax of View?
A view is a virtual table made up of data from base tables and other views, but not stored separately.
Views simplify users perception of the database (can be used to present only the necessary information while hiding details in underlying relations)
Views improve data security preventing undesired accesses Views facilite the provision of additional data independence
35. Does the View occupy memory space?No
36. Can u drop a table if it has a view?Views or tables participating in a view created with the SCHEMABINDING clause cannot be dropped. If the view is not created using SCHEMABINDING, then we can drop the table.
37. Why doesn't SQL Server permit an ORDER BY clause in the definition of a view?SQL Server excludes an ORDER BY clause from a view to comply with the ANSI SQL-92 standard. Because analyzing the rationale for this standard requires a discussion of the underlying structure of the structured query language (SQL) and the mathematics upon which it is based, we can't fully explain the restriction here. However, if you need to be able to specify an ORDER BY clause in a view, consider using the following workaround:USE pubsGO CREATE VIEW AuthorsByNameASSELECT TOP 100 PERCENT *FROM authors ORDER BY au_lname, au_fnameGOThe TOP construct, which Microsoft introduced in SQL Server 7.0, is most useful when you combine it with the ORDER BY clause. The only time that SQL Server supports an ORDER BY clause in a view is when it is used in conjunction with the TOP keyword. (Note that the TOP keyword is a SQL Server extension to the ANSI SQL-92 standard.)
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TRANSACTION 38. What is Transaction?
A transaction is a sequence of operations performed as a single logical unit of work. A logical unit of work must exhibit four properties, called the ACID (Atomicity, Consistency, Isolation, and Durability) properties, to qualify as a transaction:
Atomicity - A transaction must be an atomic unit of work; either all of its data modifications are performed or none of them is performed.
Consistency - When completed, a transaction must leave all data in a consistent state. In a relational database, all rules must be applied to the transaction's modifications to maintain all data integrity. All internal data structures, such as B-tree indexes or doubly-linked lists, must be correct at the end of the transaction.
Isolation - Modifications made by concurrent transactions must be isolated from the modifications made by any other concurrent transactions. A transaction either sees data in the state it was in before another concurrent transaction modified it, or it sees the data after the second transaction has completed, but it does not see an intermediate state. This is referred to as serializability because it results in the ability to reload the starting data and replay a series of transactions to end up with the data in the same state it was in after the original transactions were performed.
Durability - After a transaction has completed, its effects are permanently in place in the system. The modifications persist even in the event of a system failure.
39. After one Begin Transaction a truncate statement and a RollBack statements are there. Will it be rollbacked? Since the truncate statement does not perform logged operation how does it RollBack?It will rollback.**
40. Given a SQL like Begin Tran Select @@RowcountBegin Tran Select @@RowcountBegin Tran Select @@RowcountCommit Tran Select @@RowcountRollBack Select @@RowcountRollBack Select @@RowcountWhat is the value of @@Rowcount at each stmt levels?Ans : 0 – zero.@@ROWCOUNT - Returns the number of rows affected by the last statement.
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@@TRANCOUNT - Returns the number of active transactions for the current connection.Each Begin Tran will add count, each commit will reduce count and ONE rollback will make it 0.
OTHER 41. What are the constraints for Table Constraints define rules regarding
the values allowed in columns and are the standard mechanism for enforcing integrity. SQL Server 2000 supports five classes of constraints.NOT NULLCHECKUNIQUEPRIMARY KEYFOREIGN KEY
42. There are 50 columns in a table. Write a query to get first 25 columnsAns: Need to mention each column names.
43. How to list all the tables in a particular database?USE pubsGOsp_help
44. What are cursors? Explain different types of cursors. What are the disadvantages of cursors? How can you avoid cursors?Cursors allow row-by-row processing of the result sets.Types of cursors: Static, Dynamic, Forward-only, Keyset-driven.Disadvantages of cursors: Each time you fetch a row from the cursor, it results in a network roundtrip. Cursors are also costly because they require more resources and temporary storage (results in more IO operations). Further, there are restrictions on the SELECT statements that can be used with some types of cursors.How to avoid cursor:
1. Most of the times, set based operations can be used instead of cursors. Here is an example: If you have to give a flat hike to your employees using the following criteria:Salary between 30000 and 40000 -- 5000 hikeSalary between 40000 and 55000 -- 7000 hikeSalary between 55000 and 65000 -- 9000 hikeIn this situation many developers tend to use a cursor, determine each employee's salary and update his salary according to the above formula. But the same can be achieved by multiple update statements or can be combined in a single UPDATE statement as shown below:UPDATE tbl_emp SET salary =CASE WHEN salary BETWEEN 30000 AND 40000 THEN salary + 5000WHEN salary BETWEEN 40000 AND 55000 THEN salary + 7000WHEN salary BETWEEN 55000 AND 65000 THEN salary + 10000END
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2. You need to call a stored procedure when a column in a particular row meets certain condition. You don't have to use cursors for this. This can be achieved using WHILE loop, as long as there is a unique key to identify each row. For examples of using WHILE loop for row by row processing, check out the 'My code library' section of my site or search for WHILE.
8. What is Dynamic Cursor? Suppose, I have a dynamic cursor attached to table in a database. I have another means by which I will modify the table. What do you think will the values in the cursor be?Dynamic cursors reflect all changes made to the rows in their result set when scrolling through the cursor. The data values, order, and membership of the rows in the result set can change on each fetch. All UPDATE, INSERT, and DELETE statements made by all users are visible through the cursor. Updates are visible immediately if they are made through the cursor using either an API function such as SQLSetPos or the Transact-SQL WHERE CURRENT OF clause. Updates made outside the cursor are not visible until they are committed, unless the cursor transaction isolation level is set to read uncommitted.
9. What is DATEPART?Returns an integer representing the specified datepart of the specified date.
10.Difference between Delete and Truncate?TRUNCATE TABLE is functionally identical to DELETE statement with no WHERE clause: both remove all rows in the table.(1) But TRUNCATE TABLE is faster and uses fewer system and transaction log resources than DELETE. The DELETE statement removes rows one at a time and records an entry in the transaction log for each deleted row. TRUNCATE TABLE removes the data by deallocating the data pages used to store the table's data, and only the page deallocations are recorded in the transaction log.(2) Because TRUNCATE TABLE is not logged, it cannot activate a trigger.(3) The counter used by an identity for new rows is reset to the seed for the column. If you want to retain the identity counter, use DELETE instead.Of course, TRUNCATE TABLE can be rolled back.
11.Given a scenario where two operations, Delete Stmt and Truncate Stmt, where the Delete Statement was successful and the truncate stmt was failed. – Can u judge why?**
12.What are global variables? Tell me some of them?Transact-SQL global variables are a form of function and are now referred to as functions.ABS - Returns the absolute, positive value of the given numeric expression.SUMAVGAND
13.What is DDL?Data definition language (DDL) statements are SQL statements that support the definition or declaration of database objects (for example,
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CREATE TABLE, DROP TABLE, and ALTER TABLE).You can use the ADO Command object to issue DDL statements. To differentiate DDL statements from a table or stored procedure name, set the CommandType property of the Command object to adCmdText. Because executing DDL queries with this method does not generate any recordsets, there is no need for a Recordset object.
14.What is DML?Data Manipulation Language (DML), which is used to select, insert, update, and delete data in the objects defined using DDL
15.What are keys in RDBMS? What is a primary key/ foreign key?There are two kinds of keys.A primary key is a set of columns from a table that are guaranteed to have unique values for each row of that table.Foreign keys are attributes of one table that have matching values in a primary key in another table, allowing for relationships between tables.
16.What is the difference between Primary Key and Unique Key?Both primary key and unique key enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default. Another major difference is that, primary key doesn't allow NULLs, but unique key allows one NULL only.
17.Define candidate key, alternate key, composite key?A candidate key is one that can identify each row of a table uniquely. Generally a candidate key becomes the primary key of the table. If the table has more than one candidate key, one of them will become the primary key, and the rest are called alternate keys. A key formed by combining at least two or more columns is called composite key.
18.What is the Referential Integrity?Referential integrity refers to the consistency that must be maintained between primary and foreign keys, i.e. every foreign key value must have a corresponding primary key value.
19.What are defaults? Is there a column to which a default can't be bound?A default is a value that will be used by a column, if no value is supplied to that column while inserting data. IDENTITY columns and timestamp columns can't have defaults bound to them.
20.What is Query optimization? How is tuning a performance of query done?
21.What is the use of trace utility?**
22.What is the use of shell commands? xp_cmdshellExecutes a given command string as an operating-system command shell and returns any output as rows of text. Grants nonadministrative users permissions to execute xp_cmdshell.
23.What is use of shrink database?Microsoft® SQL Server 2000 allows each file within a database to be shrunk to remove unused pages. Both data and transaction log files can be shrunk.
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24. If the performance of the query suddenly decreased where you will check?
25.What is a pass-through query?Microsoft® SQL Server 2000 sends pass-through queries as un-interpreted query strings to an OLE DB data source. The query must be in a syntax the OLE DB data source will accept. A Transact-SQL statement uses the results from a pass-through query as though it is a regular table reference.This example uses a pass-through query to retrieve a result set from a Microsoft Access version of the Northwind sample database.SELECT *FROM OpenRowset('Microsoft.Jet.OLEDB.4.0', 'c:\northwind.mdb';'admin'; '', 'SELECT CustomerID, CompanyNameFROM CustomersWHERE Region = ''WA'' ')
26.How do you differentiate Local and Global Temporary table?You can create local and global temporary tables. Local temporary tables are visible only in the current session; global temporary tables are visible to all sessions. Prefix local temporary table names with single number sign (#table_name), and prefix global temporary table names with a double number sign (##table_name). SQL statements reference the temporary table using the value specified for table_name in the CREATE TABLE statement:CREATE TABLE #MyTempTable (cola INT PRIMARY KEY)INSERT INTO #MyTempTable VALUES (1)
27.How the Exists keyword works in SQL Server?USE pubsSELECT au_lname, au_fnameFROM authorsWHERE exists (SELECT * FROM publishers WHERE authors.city = publishers.city)When a subquery is introduced with the keyword EXISTS, it functions as an existence test. The WHERE clause of the outer query tests for the existence of rows returned by the subquery. The subquery does not actually produce any data; it returns a value of TRUE or FALSE.
28.ANY?USE pubsSELECT au_lname, au_fnameFROM authorsWHERE city = ANY(SELECT cityFROM publishers)
29. to select date part onlySELECT CONVERT(char(10),GetDate(),101)--to select time part onlySELECT right(GetDate(),7)
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30.How can I send a message to user from the SQL Server? You can use the xp_cmdshell extended stored procedure to run net send command. This is the example to send the 'Hello' message to JOHN:EXEC master..xp_cmdshell "net send JOHN 'Hello'"To get net send message on the Windows 9x machines, you should run the WinPopup utility. You can place WinPopup in the Startup group under Program Files.
31.What is normalization? Explain different levels of normalization? Explain Third normalization form with an example?The process of refining tables, keys, columns, and relationships to create an efficient database is called normalization. This should eliminates unnecessary duplication and provides a rapid search path to all necessary information.Some of the benefits of normalization are:
Data integrity (because there is no redundant, neglected data) Optimized queries (because normalized tables produce rapid,
efficient joins) Faster index creation and sorting (because the tables have fewer
columns) Faster UPDATE performance (because there are fewer indexes per
table) Improved concurrency resolution (because table locks will affect
less data) Eliminate redundancy
There are a few rules for database normalization. Each rule is called a "normal form." If the first rule is observed, the database is said to be in "first normal form." If the first three rules are observed, the database is considered to be in "third normal form." Although other levels of normalization are possible, third normal form is considered the highest level necessary for most applications.
1. First Normal Form (1NF) Eliminate repeating groups in individual tables Create a separate table for each set of related data. Identify each set of related data with a primary key.
Do not use multiple fields in a single table to store similar data. Example
Subordinate1 Subordinate2 Subordinate3 Subordinate4 Bob Jim Mary Beth Mary Mike Jason Carol Mark Jim Alan
Eliminate duplicative columns from the same table. Clearly, the Subordinate1-Subordinate4 columns are duplicative. What happens when we need to add or remove a subordinate?
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SubordinatesBob Jim, Mary, BethMary Mike, Jason, Carol, Mark Jim Alan
This solution is closer, but it also falls short of the mark. The subordinates column is still duplicative and non-atomic. What happens when we need to add or remove a subordinate? We need to read and write the entire contents of the table. That’s not a big deal in this situation, but what if one manager had one hundred employees? Also, it complicates the process of selecting data from the database in future queries. Solution:
Subordinate Bob Jim Bob Mary Bob Beth Mary Mike Mary Jason Mary Carol Mary Mark Jim Alan
2. Second Normal Form (2NF) Create separate tables for sets of values that apply to
multiple records. Relate these tables with a foreign key.
Records should not depend on anything other than a table's primary key (a compound key, if necessary). For example, consider a customer's address in an accounting system. The address is needed by the Customers table, but also by the Orders, Shipping, Invoices, Accounts Receivable, and Collections tables. Instead of storing the customer's address as a separate entry in each of these tables, store it in one place, either in the Customers table or in a separate Addresses table.
3. Third Normal Form (3NF) Eliminate fields that do not depend on the key .
Values in a record that are not part of that record's key do not belong in the table. In general, any time the contents of a group of fields may apply to more than a single record in the table, consider placing those fields in a separate table.For example, in an Employee Recruitment table, a candidate's university name and address may be included. But you need a complete list of universities for group mailings. If university information is stored in the Candidates table, there is no way to list universities with no current candidates. Create a separate Universities table and link it to the
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Candidates table with a university code key.Another Example :
MemberId Name Company CompanyLoc
1 John Smith ABC Alabama
2 Dave Jones MCI Florida
The Member table satisfies first normal form - it contains no repeating groups. It satisfies second normal form - since it doesn't have a multivalued key. But the key is MemberID, and the company name and location describe only a company, not a member. To achieve third normal form, they must be moved into a separate table. Since they describe a company, CompanyCode becomes the key of the new "Company" table.
The motivation for this is the same for second normal form: we want to avoid update and delete anomalies. For example, suppose no members from the IBM were currently stored in the database. With the previous design, there would be no record of its existence, even though 20 past members were from IBM!Member Table
MemberId Name CID
1 John Smith 1
2 Dave Jones 2
Company Table
CId Name Location
1 ABC Alabama
2 MCI Florida
4. Boyce-Codd Normal Form (BCNF)A relation is in Boyce/Codd normal form if and only if the only determinants are candidate key. Its a different version of 3NF, indeed, was meant to replace it. [A determinant is any attribute on which some other attribute is (fully) functionally dependent.]
5. 4th Normal Form (4NF)A table is in 4NF if it is in BCNF and if it has no multi-valued dependencies. This applies primarily to key-only associative tables, and appears as a ternary relationship, but has incorrectly merged 2 distinct, independent relationships.Eg: This could be any 2 M:M relationships from a single entity. For instance, a member could know many software tools, and a software tool may be used by many members. Also, a member could have recommended many books, and a book could be recommended by many members.
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Software
member
Book
6. The correct solution, to cause the model to be in 4th normal form, is to ensure that all M:M relationships are resolved independently if they are indeed independent.
Software
membersoftware
member
memberBook
book
7. 5th Normal Form (5NF)(PJNF)A table is in 5NF, also called "Projection-Join Normal Form", if it is in 4NF and if every join dependency in the table is a consequence of the candidate keys of the table.
8. Domain/key normal form (DKNF). A key uniquely identifies each row in a table. A domain is the set of permissible values for an attribute. By enforcing key and domain restrictions, the database is assured of being freed from modification anomalies. DKNF is the normalization level that most designers aim to achieve.
**Remember, these normalization guidelines are cumulative. For a database to be in 2NF, it must first fulfill all the criteria of a 1NF database.
32. If a database is normalized by 3 NF then how many number of tables it should contain in minimum? How many minimum if 2NF and 1 NF?
33.What is denormalization and when would you go for it?As the name indicates, denormalization is the reverse process of normalization. It's the controlled introduction of redundancy in to the database design. It helps improve the query performance as the number of joins could be reduced.
34.How can I randomly sort query results? To randomly order rows, or to return x number of randomly chosen rows, you can use the RAND function inside the SELECT statement. But the RAND function is resolved only once for the entire query, so every row will get same value. You can use an ORDER BY clause to sort the rows by the result from the NEWID function, as the following code shows:SELECT *FROM Northwind..Orders ORDER BY NEWID()
35.sp_whoProvides information about current Microsoft® SQL Server™ users and processes. The information returned can be filtered to return only those processes that are not idle.
36.Have you worked on Dynamic SQL? How will You handled “ (Double Quotes) in Dynamic SQL?
37.How to find dependents of a table?Verify dependencies with sp_depends before dropping an object
38.What is the difference between a CONSTRAINT AND RULE?Rules are a backward-compatibility feature that perform some of the same functions as CHECK constraints. CHECK constraints are the preferred,
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standard way to restrict the values in a column. CHECK constraints are also more concise than rules; there can only be one rule applied to a column, but multiple CHECK constraints can be applied. CHECK constraints are specified as part of the CREATE TABLE statement, while rules are created as separate objects and then bound to the column.
39.How to call a COM dll from SQL Server 2000?sp_OACreate - Creates an instance of the OLE object on an instance of Microsoft® SQL ServerSyntaxsp_OACreate progid, | clsid, objecttoken OUTPUT [ , context ]
context - Specifies the execution context in which the newly created OLE object runs. If specified, this value must be one of the following:1 = In-process (.dll) OLE server only4 = Local (.exe) OLE server only5 = Both in-process and local OLE server allowed
Examples
A. Use Prog ID - This example creates a SQL-DMO SQLServer object by using its ProgID.
DECLARE @object intDECLARE @hr intDECLARE @src varchar(255), @desc varchar(255)EXEC @hr = sp_OACreate 'SQLDMO.SQLServer', @object OUTIF @hr <> 0BEGIN EXEC sp_OAGetErrorInfo @object, @src OUT, @desc OUT SELECT hr=convert(varbinary(4),@hr), Source=@src, Description=@desc RETURNEND
B. Use CLSID - This example creates a SQL-DMO SQLServer object by using its CLSID.
DECLARE @object intDECLARE @hr intDECLARE @src varchar(255), @desc varchar(255)EXEC @hr = sp_OACreate '{00026BA1-0000-0000-C000-000000000046}', @object OUTIF @hr <> 0BEGIN EXEC sp_OAGetErrorInfo @object, @src OUT, @desc OUT SELECT hr=convert(varbinary(4),@hr), Source=@src, Description=@desc
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RETURNEND
40.Difference between sysusers and syslogins?sysusers - Contains one row for each Microsoft® Windows user, Windows group, Microsoft SQL Server™ user, or SQL Server role in the database.syslogins - Contains one row for each login account.
41.What is the row size in SQL Server 2000?8060 bytes.
42.How will you find structure of table, all tables/views in one db, all dbs?//structure of tablesp_helpdb tbl_emp
//list of all databasessp_helpdbORSELECT * FROM master.dbo.sysdatabases
//details about database pubs. .mdf, .ldf file locations, size of databasesp_helpdb pubs
//lists all tables under current databasesp_tablesORSELECT * FROM information_schema.tables WHERE (table_type = 'base table')ORSELECT * FROM sysobjects WHERE type = 'U' //faster
43.B-tree indexes or doubly-linked lists? 44.What is the system function to get the current user's user id?
USER_ID(). Also check out other system functions like USER_NAME(), SYSTEM_USER, SESSION_USER, CURRENT_USER, USER, SUSER_SID(), HOST_NAME().
45.What are the series of steps that happen on execution of a query in a Query Analyzer?1) Syntax checking 2) Parsing 3) Execution plan
46.Which event (Check constraints, Foreign Key, Rule, trigger, Primary key check) will be performed last for integrity check?Identity Insert CheckNullability constraintData type checkInstead of triggerPrimary keyCheck constraintForeign keyDML Execution (update statements)After Trigger**
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47.How will you show many to many relation in sql?Create 3rd table with 2 columns which having one to many relation to these tables.
48.When a query is sent to the database and an index is not being used, what type of execution is taking place?A table scan.
49.What is #, ##, @, @@ means?@@ - System variables@ - user defined variables
50.What is the difference between a Local temporary table and a Global temporary table? How is each one denoted?Local temporary table will be accessible to only current user session, its name will be preceded with a single hash (#mytable)Global temporary table will be accessible to all users, & it will be dropped only after ending of all active connections, its name will be preceded with double hash (##mytable)
51.What is covered queries in SQL Server? 52.What is HASH JOIN, MERGE JOIN?
TOOLS 53.Have you ever used DBCC command? Give an example for it.
The Transact-SQL programming language provides DBCC statements that act as Database Console Commands for Microsoft® SQL Serve 2000. These statements check the physical and logical consistency of a database. Many DBCC statements can fix detected problems. Database Console Command statements are grouped into these categories.
Statement category Perform
Maintenance statements
Maintenance tasks on a database, index, or filegroup.
Miscellaneous statements
Miscellaneous tasks such as enabling row-level locking or removing a dynamic-link library (DLL) from memory.
Status statements Status checks.
Validation statements
Validation operations on a database, table, index, catalog, filegroup, system tables, or allocation of database pages.
DBCC CHECKDB, DBCC CHECKTABLE, DBCC CHECKCATALOG, DBCC CHECKALLOC, DBCC SHOWCONTIG, DBCC SHRINKDATABASE, DBCC SHRINKFILE etc.
54.How do you use DBCC statements to monitor various aspects of a SQL server installation?**
55.What is the output of DBCC Showcontig statement?Displays fragmentation information for the data and indexes of the specified table.
56.How do I reset the identity column?You can use the DBCC CHECKIDENT statement, if you want to reset or reseed the identity column. For example, if you need to force the current identity value in the jobs table to a value of 100, you can use the following:
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USE pubsGODBCC CHECKIDENT (jobs, RESEED, 100)GO
57.About SQL Command line executables
Utilities
bcpconsoleisqlsqlagentsqldiagsqlmaintsqlservrvswitch
dtsrundtswizisqlwitwizodbccmptosqlrebuildmsqlftwiz
distriblogreadreplmergsnapshot
scm
regxmlss
58.What is DTC?The Microsoft Distributed Transaction Coordinator (MS DTC) is a transaction manager that allows client applications to include several different sources of data in one transaction. MS DTC coordinates committing the distributed transaction across all the servers enlisted in the transaction.
59.What is DTS? Any drawbacks in using DTS?Microsoft® SQL Server™ 2000 Data Transformation Services (DTS) is a set of graphical tools and programmable objects that lets you extract, transform, and consolidate data from disparate sources into single or multiple destinations.
60.What is BCP?The bcp utility copies data between an instance of Microsoft® SQL Server™ 2000 and a data file in a user-specified format.C:\Documents and Settings\sthomas>bcpusage: bcp {dbtable | query} {in | out | queryout | format} datafile[-m maxerrors] [-f formatfile] [-e errfile][-F firstrow] [-L lastrow] [-b batchsize][-n native type] [-c character type] [-w wide character type]
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[-N keep non-text native] [-V file format version] [-q quoted identifier][-C code page specifier] [-t field terminator] [-r row terminator][-i inputfile] [-o outfile] [-a packetsize][-S server name] [-U username] [-P password][-T trusted connection] [-v version] [-R regional enable][-k keep null values] [-E keep identity values][-h "load hints"]
61.How can I create a plain-text flat file from SQL Server as input to another application?One of the purposes of Extensible Markup Language (XML) is to solve challenges like this, but until all applications become XML-enabled, consider using our faithful standby, the bulk copy program (bcp) utility. This utility can do more than just dump a table; bcp also can take its input from a view instead of from a table. After you specify a view as the input source, you can limit the output to a subset of columns or to a subset of rows by selecting appropriate filtering (WHERE and HAVING) clauses.More important, by using a view, you can export data from multiple joined tables. The only thing you cannot do is specify the sequence in which the rows are written to the flat file, because a view does not let you include an ORDER BY clause in it unless you also use the TOP keyword.If you want to generate the data in a particular sequence or if you cannot predict the content of the data you want to export, be aware that in addition to a view, bcp also supports using an actual query. The only "gotcha" about using a query instead of a table or view is that you must specify queryout in place of out in the bcp command line.For example, you can use bcp to generate from the pubs database a list of authors who reside in California by writing the following code:bcp "SELECT * FROM pubs..authors WHERE state = 'CA'" queryout c:\CAauthors.txt -c -T -S
62.What are the different ways of moving data/databases between servers and databases in SQL Server? There are lots of options available, you have to choose your option depending upon your requirements. Some of the options you have are: BACKUP/RESTORE, detaching and attaching databases, replication, DTS, BCP, logshipping, INSERT...SELECT, SELECT...INTO, creating INSERT scripts to generate data.
63.How will I export database?Through DTS - Import/Export wizardBackup - through Complete/Differential/Transaction Log
64.How to export database at a particular time, every week?Backup - ScheduleDTS - ScheduleJobs - create a new job
65.How do you load large data to the SQL server database?bcp
66.How do you transfer data from text file to database (other than DTS)?bcp
67.What is OSQL and ISQL utility?The osql utility allows you to enter Transact-SQL statements, system procedures, and script files. This utility uses ODBC to communicate with
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the server. The isql utility allows you to enter Transact-SQL statements, system procedures, and script files; and uses DB-Library to communicate with Microsoft® SQL Server™ 2000.All DB-Library applications, such as isql, work as SQL Server 6.5–level clients when connected to SQL Server 2000. They do not support some SQL Server 2000 features.The osql utility is based on ODBC and does support all SQL Server 2000 features. Use osql to run scripts that isql cannot run.
68.What Tool you have used for checking Query Optimization? What is the use of profiler in sql server? What is the first thing u look at in a SQL Profiler?SQL Profiler is a graphical tool that allows system administrators to monitor events in an instance of Microsoft® SQL Server™. You can capture and save data about each event to a file or SQL Server table to analyze later. For example, you can monitor a production environment to see which stored procedures is hampering performance by executing too slowly. Use SQL Profiler to:
Monitor the performance of an instance of SQL Server. Debug Transact-SQL statements and stored procedures. Identify slow-executing queries. Test SQL statements and stored procedures in the development
phase of a project by single-stepping through statements to confirm that the code works as expected.
Troubleshoot problems in SQL Server by capturing events on a production system and replaying them on a test system. This is useful for testing or debugging purposes and allows users to continue using the production system without interference.
Audit and review activity that occurred on an instance of SQL Server. This allows a security administrator to review any of the auditing events, including the success and failure of a login attempt and the success and failure of permissions in accessing statements and objects.
Permissions
45. A user is a member of Public role and Sales role. Public role has the permission to select on all the table, and Sales role, which doesn’t have a select permission on some of the tables. Will that user be able to select from all tables?**
46. If a user does not have permission on a table, but he has permission to a view created on it, will he be able to view the data in table?Yes.
47. Describe Application Role and explain a scenario when you will use it?**
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48. After removing a table from database, what other related objects have to be dropped explicitly?(view, SP)
49. You have a SP names YourSP and have the a Select Stmt inside the SP. You also have a user named YourUser. What permissions you will give him for accessing the SP.**
50. Different Authentication modes in Sql server? If a user is logged under windows authentication mode, how to find his userid?There are Three Different authentication modes in sqlserver.
1. Windows Authentication Mode 2. SqlServer Authentication Mode 3. Mixed Authentication Mode
“system_user” system function in sqlserver to fetch the logged on user name.
69.Give the connection strings from front-end for both type logins(windows,sqlserver)?This are specifically for sqlserver not for any other RDBMSData Source=MySQLServer;Initial Catalog=NORTHWIND;Integrated Security=SSPI (windows)Data Source=MySQLServer;Initial Catalog=NORTHWIND;Uid=” ”;Pwd=” ”(sqlserver)
70.What are three SQL keywords used to change or set someone’s permissions?Grant, Deny and Revoke
Administration 71.Explain the architecture of SQL Server?
** 72.Different types of Backups?
o A full database backup is a full copy of the database. o A transaction log backup copies only the transaction log. o A differential backup copies only the database pages modified after
the last full database backup. o A file or filegroup restore allows the recovery of just the portion of a
database that was on the failed disk.
49.What are ‘jobs’ in SQL Server? How do we create one? What is tasks?Using SQL Server Agent jobs, you can automate administrative tasks and run them on a recurring basis.**
50.What is database replication? What are the different types of replication you can set up in SQL Server? How are they used? What is snapshot replication how is it different from Transactional
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replication?Replication is the process of copying/moving data between databases on the same or different servers. SQL Server supports the following types of replication scenarios:
1. Snapshot replication - It distributes data exactly as it appears at a specific moment in time and doesn’t monitor for updates. It can be used when data changes are infrequent. It is often used for browsing data such as price lists, online catalog, or data for decision support where the current data is not required and data is used as read only.
2. Transactional replication (with immediate updating subscribers, with queued updating subscribers) - With this an initial snapshot of data is applied, and whenever data modifications are made at the publisher, the individual transactions are captured and propagated to the subscribers.
3. Merge replication - It is the process of distributing the data between publisher and subscriber, it allows the publisher and subscriber to update the data while connected or disconnected, and then merging the updates between the sites when they are connected.
73.How can u look at what are the process running on SQL server? How can you kill a process in SQL server?
o Expand a server group, and then expand a server. o Expand Management, and then expand Current Activity. o Click Process Info. The current server activity is displayed in the
details pane.
In the details pane, right-click a Process ID, and then click Kill Process.
51.What is RAID and what are different types of RAID configurations? RAID stands for Redundant Array of Inexpensive Disks, used to provide fault tolerance to database servers. There are six RAID levels 0 through 5 offering different levels of performance, fault tolerance.
52.Some of the tools/ways that help you troubleshooting performance problems are: SET SHOWPLAN_ALL ON, SET SHOWPLAN_TEXT ON, SET STATISTICS IO ON, SQL Server Profiler, Windows NT /2000 Performance monitor, Graphical execution plan in Query Analyzer.
53.How to determine the service pack currently installed on SQL Server? The global variable @@Version stores the build number of the sqlservr.exe, which is used to determine the service pack installed.eg: Microsoft SQL Server 2000 - 8.00.760 (Intel X86) Dec 17 2002 14:22:05 Copyright (c) 1988-2003 Microsoft Corporation Enterprise Edition on Windows NT 5.0 (Build 2195: Service Pack 3)
54.What is the purpose of using COLLATE in a query?The term, collation, refers to a set of rules that determine how data is sorted and compared. In Microsoft® SQL Server 2000, it is not required to
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separately specify code page and sort order for character data, and the collation used for Unicode data. Instead, specify the collation name and sorting rules to use. Character data is sorted using rules that define the correct character sequence, with options for specifying case-sensitivity, accent marks, kana character types, and character width. Microsoft SQL Server 2000 collations include these groupings:
Windows collations - Windows collations define rules for storing character data based on the rules defined for an associated Windows locale. The base Windows collation rules specify which alphabet or language is used when dictionary sorting is applied, as well as the code page used to store non-Unicode character data. For Windows collations, the nchar, nvarchar, and ntext data types have the same sorting behavior as char, varchar, and text data types
SQL collations - SQL collations are provided for compatibility with sort orders in earlier versions of Microsoft SQL Server.
Sort OrderBinary is the fastest sorting order, and is case-sensitive. If Binary is selected, the Case-sensitive, Accent-sensitive, Kana-sensitive, and Width-sensitive options are not available.
Sort order Description
Binary Sorts and compares data in Microsoft® SQL Server™ tables based on the bit patterns defined for each character. Binary sort order is case-sensitive, that is lowercase precedes uppercase, and accent-sensitive. This is the fastest sorting order. If this option is not selected, SQL Server follows sorting and comparison rules as defined in dictionaries for the associated language or alphabet.
Case-sensitive
Specifies that SQL Server distinguish between uppercase and lowercase letters. If not selected, SQL Server considers the uppercase and lowercase versions of letters to be equal. SQL Server does not define whether lowercase letters sort lower or higher in relation to uppercase letters when Case-sensitive is not selected.
Accent-sensitive
Specifies that SQL Server distinguish between accented and unaccented characters. For example, 'a' is not equal to 'á'. If not selected, SQL Server considers the accented and unaccented versions of letters to be equal.
Kana-sensitive
Specifies that SQL Server distinguish between the two types of Japanese kana characters: Hiragana and Katakana. If not selected, SQL Server considers Hiragana and Katakana characters to be equal.
Width- Specifies that SQL Server distinguish between a single-byte
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sensitive character (half-width) and the same character when represented as a double-byte character (full-width). If not selected, SQL Server considers the single-byte and double-byte representation of the same character to be equal.
Windows collation options:
Use Latin1_General for the U.S. English character set (code page 1252).
Use Modern_Spanish for all variations of Spanish, which also use the same character set as U.S. English (code page 1252).
Use Arabic for all variations of Arabic, which use the Arabic character set (code page 1256).
Use Japanese_Unicode for the Unicode version of Japanese (code page 932), which has a different sort order from Japanese, but the same code page (932).
51. What is the STUFF Function and how does it differ from the REPLACE function?STUFF - Deletes a specified length of characters and inserts another set of characters at a specified starting point. SELECT STUFF('abcdef', 2, 3, 'ijklmn')GOHere is the result set:--------- aijklmnef
REPLACE - Replaces all occurrences of the second given string expression in the first string expression with a third expression.SELECT REPLACE('abcdefghicde','cde','xxx')GO Here is the result set: ------------abxxxfghixxx
52. What does it mean to have quoted_identifier on? What are the implications of having it off?When SET QUOTED_IDENTIFIER is OFF (default), literal strings in expressions can be delimited by single or double quotation marks.When SET QUOTED_IDENTIFIER is ON, all strings delimited by double quotation marks are interpreted as object identifiers. Therefore, quoted identifiers do not have to follow the Transact-SQL rules for identifiers. SET QUOTED_IDENTIFIER must be ON when creating or manipulating indexes on computed columns or indexed views. If SET QUOTED_IDENTIFIER is OFF, CREATE, UPDATE, INSERT, and DELETE statements on tables with indexes on computed columns or indexed views will fail. The SQL Server ODBC driver and Microsoft OLE DB Provider for SQL Server automatically set QUOTED_IDENTIFIER to ON when connecting.When a stored procedure is created, the SET QUOTED_IDENTIFIER and
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SET ANSI_NULLS settings are captured and used for subsequent invocations of that stored procedure. When executed inside a stored procedure, the setting of SET QUOTED_IDENTIFIER is not changed.SET QUOTED_IDENTIFIER OFFGO-- Attempt to create a table with a reserved keyword as a name-- should fail.CREATE TABLE "select" ("identity" int IDENTITY, "order" int)GO
SET QUOTED_IDENTIFIER ONGO-- Will succeed.CREATE TABLE "select" ("identity" int IDENTITY, "order" int)GO
53. What is the purpose of UPDATE STATISTICS?Updates information about the distribution of key values for one or more statistics groups (collections) in the specified table or indexed view.
54. Fundamentals of Data warehousing & olap? 55. What do u mean by OLAP server? What is the difference between
OLAP and OLTP? 56. What is a tuple?
A tuple is an instance of data within a relational database. 57. Services and user Accounts maintenance 58. sp_configure commands?
Displays or changes global configuration settings for the current server. 59. What is the basic functions for master, msdb, tempdb databases?
Microsoft® SQL Server 2000 systems have four system databases: master - The master database records all of the system level
information for a SQL Server system. It records all login accounts and all system configuration settings. master is the database that records the existence of all other databases, including the location of the database files.
tempdb - tempdb holds all temporary tables and temporary stored procedures. It also fills any other temporary storage needs such as work tables generated by SQL Server. tempdb is re-created every time SQL Server is started so the system starts with a clean copy of the database. By default, tempdb autogrows as needed while SQL Server is running. If the size defined for tempdb is small, part of your system processing load may be taken up with autogrowing tempdb to the size needed to support your workload each time to restart SQL Server. You can avoid this overhead by using ALTER DATABASE to increase the size of tempdb.
model - The model database is used as the template for all databases created on a system. When a CREATE DATABASE statement is issued, the first part of the database is created by copying in the contents of the model database, then the remainder of the new database is filled with empty pages. Because tempdb is
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created every time SQL Server is started, the model database must always exist on a SQL Server system.
msdb - The msdb database is used by SQL Server Agent for scheduling alerts and jobs, and recording operators.
60. What are sequence diagrams? What you will get out of this sequence diagrams?Sequence diagrams document the interactions between classes to achieve a result, such as a use case. Because UML is designed for object-oriented programming, these communications between classes are known as messages. The sequence diagram lists objects horizontally, and time vertically, and models these messages over time.
61. What are the new features of SQL 2000 than SQL 7? What are the new datatypes in sql?
XML Support - The relational database engine can return data as Extensible Markup Language (XML) documents. Additionally, XML can also be used to insert, update, and delete values in the database. (for xml raw - to retrieve output as xml type)
User-Defined Functions - The programmability of Transact-SQL can be extended by creating your own Transact-SQL functions. A user-defined function can return either a scalar value or a table.
Indexed Views - Indexed views can significantly improve the performance of an application where queries frequently perform certain joins or aggregations. An indexed view allows indexes to be created on views, where the result set of the view is stored and indexed in the database.
New Data Types - SQL Server 2000 introduces three new data types. bigint is an 8-byte integer type. sql_variant is a type that allows the storage of data values of different data types. table is a type that allows applications to store results temporarily for later use. It is supported for variables, and as the return type for user-defined functions.
INSTEAD OF and AFTER Triggers - INSTEAD OF triggers are executed instead of the triggering action (for example, INSERT, UPDATE, DELETE). They can also be defined on views, in which case they greatly extend the types of updates a view can support. AFTER triggers fire after the triggering action. SQL Server 2000 introduces the ability to specify which AFTER triggers fire first and last.
Multiple Instances of SQL Server - SQL Server 2000 supports running multiple instances of the relational database engine on the same computer. Each computer can run one instance of the relational database engine from SQL Server version 6.5 or 7.0, along with one or more instances of the database engine from SQL Server 2000. Each instance has its own set of system and user databases.
Index Enhancements - You can now create indexes on computed columns. You can specify whether indexes are built in ascending or descending order, and if the database engine should use parallel scanning and sorting during index creation.
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62. How do we open SQL Server in single user mode?We can accomplish this in any of the three ways given below :-
a. From Command Prompt :-sqlservr -m
b. From Startup Options :-Go to SQL Server Properties by right-clicking on the Server name in the Enterprise manager. Under the 'General' tab, click on 'Startup Parameters'. Enter a value of -m in the Parameter.
c. From Registry :-Go to HKEY_LOCAL_MACHINE\Software\Microsoft\MSSQLServer\MSSQLServer\Parameters. Add new string value. Specify the 'Name' as SQLArg(n) & 'Data' as -m. Where n is the argument number in the list of arguments.
6. Difference between clustering and NLB (Network Load Balancing)?**
7. Explain Active/Active and Active/Passive cluster configurations?**
8. What is Log Shipping?In Microsoft® SQL Server™ 2000 Enterprise Edition, you can use log shipping to feed transaction logs from one database to another on a constant basis. Continually backing up the transaction logs from a source database and then copying and restoring the logs to a destination database keeps the destination database synchronized with the source database. This allows you to have a backup server and also provides a way to offload query processing from the main computer (the source server) to read-only destination servers.
9. What are the main steps you take care for enhancing SQL Server performance?**
10.You have to check whether any users are connected to sql server database and if any user is connected to database, you have to disconnect the user(s) and run a process in a job. How do you do the above in a job?**
XML 11.How can I convert data in a Microsoft Access table into XML format?
The following applications can help you convert Access data into XML format: Access 2002, ADO 2.5, and SQLXML. Access 2002 (part of Microsoft Office XP) enables you to query or save a table in XML format. You might be able to automate this process. ADO 2.5 and later enables you to open the data into a recordset, then persist the recordset in XML format, as the following code shows:rs.Save "c:\rs.xml", adPersistXMLYou can use linked servers to add the Access database to your SQL Server 2000 database so you can run queries from within SQL Server to
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retrieve data. Then, through HTTP, you can use the SQLXML technology to extract the Access data in the XML format you want.
NEW12.@@IDENTITY ?
Ans: Returns the last-inserted identity value. 13. If a job is fail in sql server, how do find what went wrong? 14.Have you used Error handling in DTS?
http://www.smartdraw.com/resources/centers/software/erd.htm ER Diagram
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