Final Review

Dr. Bernard Chen Ph.D.University of Central Arkansas

Adding a New Column to an Existing Table The general syntax to add a

column to an existing table is

ALTER TABLE tablename

ADD columnname datatype;

SQL> ALTER TABLE student 2 ADD SocialSecurity CHAR(9);Table altered.SQL>

Modifying an Existing Column The general syntax to modify an existing column is

ALTER TABLE tablenameMODIFY columnname newdatatype;

where newdatatype is the new data type or the new size for the column.

SQL> ALTER TABLE student 2 MODIFY SocialSecurity VARCHAR2(11);Table altered.SQL>

Adding a Constraint To add a constraint using ALTER TABLE, the

syntax for table level constraint is used. The general syntax of ALTER TABLE is

ALTER TABLE tablenameADD [CONSTRAINT constraint_name]

constraint_type (column, …),

SQL> ALTER TABLE COURSE 2 ADD CONSTRAINT COURSE_PREREQ_FK FOREIGN KEY (PREREQ) 3 REFERENCES COURSE(COURSEID);Table altered.SQL>

Displaying Table Information When a user creates a table or many

tables in the database, Oracle tracks them using its own data dictionary

Viewing a User’s Table NamesSELECT TABLE_NAME FROM USER_TABLES;

To display all information:SELECT * FROM USER_TABLES;

Dropping a Column The general syntax is

ALTER TABLE tablename DROP COLUMN columnname;

Dropping a Table The general syntax is

DROP TABLE tablename [CASCADE CONSTRAINTS];

For example,DROP TABLE sample;

Oracle displays a “Table dropped” message when a table is successfully dropped.

If you add optional CASCADE CONSTRAINTS clause, it removes foreign key references to the table also.

ADDING A NEW ROW/RECORD There are two methods for inserting a NULL

value in a column.

1. Implicit Method. In the implicit method, the column’s name is omitted from the column list in an INSERT statement. For example,

INSERT INTO dept (DeptId, DeptName)

VALUES (50, ‘Production’);

ADDING A NEW ROW/RECORD

2. Explicit Method. In the explicit method, the value NULL is used as a value for numeric column, and an empty string (‘’) is used for date or character columns. For example,

INSERT INTO dept (DeptId, DeptName, Location, EmployeeId)VALUES (60, ‘Personnel’, ‘Chicago’, NULL);

UPDATING EXISTING ROWS/RECORDS The condition is optional, but it is

necessary

Suppose the student with ID 00103 in the IU college’s database switches major from BS---CS to BS---EE

UPDATE studentSet MajorID = 700Where studentid=‘00103’

DELETING EXISTING ROWS/RECORDS

Example:

DELETE FROM deptWHERE DeptID = 70

Major Outlines

Relational Algebra Relational algebra is the basic set of

operations for the relational model These operations enable a user to

specify basic retrieval requests (or queries)

Data Management and Retrieval Languages

Relational Algebra Overview Relational Algebra consists of several groups of

operations Unary Relational Operations

SELECT (symbol: (sigma)) PROJECT (symbol: (pi)) RENAME (symbol: (rho))

Relational Algebra Operations From Set Theory UNION ( ), INTERSECTION ( ), DIFFERENCE (or MINUS,

– ) CARTESIAN PRODUCT ( x )

Binary Relational Operations JOIN (several variations of JOIN exist) DIVISION

Additional Relational Operations AGGREGATE FUNCTIONS

SELECT

The SELECT operation (denoted by (sigma)) is used to select a subset of the tuples from a relation based on a selection condition

The selection condition acts as a filter Keeps only those tuples that satisfy the

qualifying condition Tuples satisfying the condition are selected

whereas the other tuples are discarded (filtered out)

SELECT

For example, to select the tuples for all employees who either work in department 4 and make over $25000 per year, or work in department 5 and make over $30000, the select operation should be:

(DNO=4 AND Salary>25000 ) OR (DNO=5 AND Salary>30000 ) (EMPLOYEE)

PROJECT PROJECT Operation is denoted by (pi)

If we are interested in only certain attributes of relation, we use PROJECT

This operation keeps certain columns (attributes) from a relation and discards the other columns.

PROJECT

Example: To list each employee’s first and last name and salary, the following is used:

LNAME, FNAME,SALARY(EMPLOYEE)

RENAME The RENAME operator is denoted by

(rho)

In some cases, we may want to rename the attributes of a relation or the relation name or both Useful when a query requires multiple

operations Necessary in some cases (see JOIN

operation later)

RENAME The general RENAME operation can be

expressed by any of the following forms: S(R) changes:

the relation name only to S

(B1, B2, …, Bn )(R) changes: the column (attribute) names only to B1, B1,

…..Bn

S (B1, B2, …, Bn )(R) changes both: the relation name to S, and the column (attribute) names to B1, B1, …..Bn

Relational Algebra Operations from Set Theory

Union

Intersection

Minus

Cartesian Product

UNION

It is a Binary operation, denoted by

The result of R S, is a relation that includes all tuples that are either in R or in S or in both R and S

Duplicate tuples are eliminated

INTERSECTION INTERSECTION is denoted by

The result of the operation R S, is a relation that includes all tuples that are in both R and S The attribute names in the result will be the

same as the attribute names in R

The two operand relations R and S must be “type compatible”

SET DIFFERENCE SET DIFFERENCE (also called MINUS or

EXCEPT) is denoted by –

The result of R – S, is a relation that includes all tuples that are in R but not in S The attribute names in the result will be

the same as the attribute names in R

The two operand relations R and S must be “type compatible”

Example to illustrate the result of UNION, INTERSECT, and DIFFERENCE

CARTESIAN PRODUCT CARTESIAN PRODUCT Operation

This operation is used to combine tuples from two relations in a combinatorial fashion.

Denoted by R(A1, A2, . . ., An) x S(B1, B2, . . ., Bm)

Result is a relation Q with degree n + m attributes: Q(A1, A2, . . ., An, B1, B2, . . ., Bm), in that order.

if R has nR tuples (denoted as |R| = nR ), and S has nS tuples, then R x S will have nR * nS tuples.

JOIN JOIN Operation (denoted by )

The sequence of CARTESIAN PRODECT followed by SELECT is used quite commonly to identify and select related tuples from two relations

This operation is very important for any relational database with more than a single relation, because it allows us combine related tuples from various relations

JOIN Consider the following JOIN operation:

If R(A1, A2, . . ., An) and S(B1, B2, . . ., Bm) Think about R.Ai=S.Bj

Result is a relation Q with degree n + m attributes: Q(A1, A2, . . ., An, B1, B2, . . ., Bm), in that order.

The resulting relation state has one tuple for each combination of tuples—r from R and s from S, but only if they satisfy the join condition r[Ai]=s[Bj]

Hence, if R has nR tuples, and S has nS tuples, then the join result will generally have less than nR * nS tuples.

EQUIJOIN The most common use of join involves join

conditions with equality comparisons only

Such a join, where the only comparison operator used is =, is called an EQUIJOIN

The JOIN seen in the previous example was an EQUIJOIN

JOIN The general case of JOIN operation is

called a Theta-join: R theta S

The join condition is called theta

Theta can be any general boolean expression on the attributes of R and S; for example: R.Ai<S.Bj AND (R.Ak=S.Bl OR R.Ap<S.Bq)

NATURAL JOIN

Another variation of JOIN called NATURAL JOIN — denoted by *

It was created to get rid of the second (superfluous) attribute in an EQUIJOIN condition.

NATURAL JOIN Another variation of JOIN called NATURAL JOIN —

denoted by *

Example: To apply a natural join on the DNUMBER attributes of DEPARTMENT and DEPT_LOCATIONS, it is sufficient to write:

DEPT_LOCS DEPARTMENT * DEPT_LOCATIONS

Only attribute with the same name is DNUMBER

An implicit join condition is created based on this attribute:

DEPARTMENT.DNUMBER=DEPT_LOCATIONS.DNUMBER

Generalized Projection It extend the projection by allowing

functions of attributes to be included in the projection list.

The general form is: F1, F2, …, Fn (R) where F1, F2,…Fn are functions over the attributes

Generalized Projection For example Consider the relation

Employee (Ssn, salary, Deduction, Year_service)

A report may be required to show:Net_salary = salary – DeductionBonus = 2000 * year_serviceTax = Salary * 25%

Then a generalized projection combined with renaming may be:

Report (Ssn, Net_salary, Bonus, Tax )

( Ssn, salary-deduction, 2000*years_service, salary*25% (R))

Aggregate Functions and Grouping A type of request that cannot be

expressed in the basic relational algebra is to specify mathematical aggregate functions on collections of values from the database.

Examples of such functions include retrieving the average or total salary of all employees or the total number of employee tuples.

Aggregate Functions and Grouping

Common functions applied to collections of numeric values include SUM, AVERAGE, MAXIMUM, and

MINIMUM.

The COUNT function is used for counting tuples or values.

Aggregate Functions and Grouping Grouping can be combined with Aggregate

Functions

Example: For each department, retrieve the DNO, COUNT SSN, and AVERAGE SALARY

A variation of aggregate operation Ʒ allows this:

Grouping attribute placed to left of symbol Aggregate functions to right of symbol

DNO Ʒ COUNT SSN, AVERAGE Salary (EMPLOYEE)

Examples of applying aggregate functions and grouping

Examples of Queries in Relational Algebra Q1: Retrieve the name and address of all employees who work for

the ‘Research’ department. Q2: For every project located in “Stafford”, list the project

number, the controlling department number, and the department manager’s last name, address, and Bdate

Q3: Find the names of employees who work on all the projects controlled by department number 4

Q4: Make a list of project numbers for projects that involve an employee whose last name is “Smith”, either as a worker or as a manager of the department that controls the project

Q5: List the names of all employees with two or more dependents Q6: Retrieve the names of employees who have no dependents. Q7: List the names of managers who have at least one dependent

Major Outlines

Relational Algebra

Data Management and Retrieval Languages

DATA MANIPULATION LANGUAGE (DML)

SQL language’s Data Manipulation Language (DML) consists of three statements: INSERT UPDATE DELETE

ADDING A NEW ROW/RECORD If you do enter column names, they do

not have to be in the same order as they were defined in table’s structure at the time of creation.

INSERT INTO student (StudentID, LAST, FIRST, ZIP, Bdate, FacultyID)

VALUES (‘00100’, ‘Will’, ‘Smith’, ‘72034’, ’12-FEB-80’, 123)

UPDATING EXISTING ROWS/RECORDS The condition is optional, but it is

necessary

Suppose the student with ID 00103 in the IU college’s database switches major from BS---CS to BS---EE

UPDATE studentSet MajorID = 700Where studentid=‘00103’

DELETING EXISTING ROWS/RECORDS Deletion is another data

maintenance operation.  In Oracle, the SQL statement

DELETE is used for deleting unwanted rows. Its general syntax is

DELETE FROM deptWHERE DeptID = 70

RETRIEVING DATA FROM A TABLE The main purpose of the SQL language

is for querying the database

The most important statement or query is the SELECT query

 The general syntax isSELECT columnlistFROM tablename;

RETRIEVING DATA FROM A TABLERESTRICTING DATA WITH A WHERE CLAUSE A WHERE clause is used with the SELECT

query to restrict rows picked

The general syntax of the WHERE clause is

SELECT columnlistFROM tablename[WHERE condition(s)];

RETRIEVING DATA FROM A TABLE The ORDER BY clause is used with the SELECT query

to sort rows in a table. 

The general syntax isSELECT columnlistFROM tablename[WHERE condition(s)][ORDER BY column|expression [ASC|

DESC]];

Grouping Data The GROUP BY clause is used for

grouping data. The general syntax is

SELECT column, groupfunction (column)

FROM tablename[WHERE condition(s)][GROUP BY column|expression][ORDER BY column|expression [ASC|DESC]];

Equijoin

SELECT student.Last STUDENT, faculty.Name

Faculty

FROM student, faculty WHERE student.FacultyID = faculty.FacultyID

Multiple Joins SELECT e.Lname EMPLOYEE,

d.DeptName Department, q.QualDesc QUALIFICATION

FROM EMPLOYEE e, Department d, QUALIFICATION q

WHERE e.DeptID = d.DeptID AND e.QualID = q.QualID

Creating a table using a subquery You can create a table by using a

nested SELECT query. The Query will create a new table and

populated it with the rows selected from the other table.

CREATE TABLE tablenameASSELECT query

Convert

Group Functions

Join

Set Theory Union Intersect Minus

Generally, the syntax would looks like:QuerySet OperationQuery