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Dr. Chen, Oracle Database System (Oracle) 1
Chapter 6Additional Database Objects
(up to p.195 and all in the pptx file)
Jason C. H. Chen, Ph.D.
Professor of MIS
School of Business
Gonzaga University
Spokane, WA 99258 USA
Dr. Chen, Oracle Database System (Oracle) 2
Objectives• Define the purpose of a sequence and state how it can
be used in a database• Explain why gaps may appear in the integers
generated by a sequence• Use the CREATE SEQUENCE command to create a
sequence• Call and use sequence values• Identify which options cannot be changed by the
ALTER SEQUENCE command• Delete a sequence• Create indexes with the CREATE INDEX command• Explain the main index structures: B-tree and bitmap
Dr. Chen, Oracle Database System (Oracle) 3
Objectives (continued)• Verify index use with the explain plan• Introduce variations on conventional indexes,
including a function-based index and an index organized table
• Verify index existence via the data dictionary• Rename an index with the ALTER INDEX
command• Remove an index using the DROP INDEX
command• Create and remove a public synonym
Dr. Chen, Oracle Database System (Oracle) 4
Database Objects• An object is anything that has a name and
defined structure• Includes:
– Table – stores data– Sequence – generates sequential integers– Index – allows users to quickly locate specific
records– Synonym – alias for other database objects
Dr. Chen, Oracle Database System (Oracle) 5
Sequences• Used for internal control purposes by
providing sequential integers for auditing• Used to generate unique value for primary
key column– Surrogate key = no correlation with actual row
contents
Dr. Chen, Oracle Database System (Oracle) 6
Creating a Sequence
• Use the CREATE SEQUENCE command • Various intervals are allowed – Default: 1• You can specify the starting number – Default: 1
CREATE SEQUENCE sequencename[INCREASE BY value][START WITH value][{MAXVALUE value | MAXVALUE}][{MINVALUE value | MINVALUE}][{CYCLE | NOCYLE}][{ORDER | NOORDER}][{CACHE value | NOCACHE}];
Figure 6-1 Syntax of the CREATE SEQUENCE command
Dr. Chen, Oracle Database System (Oracle) 7
Creating a Sequence (continued)
• Can specify MINVALUE for decreasing sequence and MAXVALUE for increasing sequence
• Numbers can be reused if CYCLE is specified– The options determine whether Oracle should begin
reissuing values from the sequence after reaching the minimum or maximum value.
• ORDER clause is used in application cluster environment
• Use CACHE to pregenerate integers – Default: 20
Dr. Chen, Oracle Database System (Oracle) 8
ORDERS Data Files
Dr. Chen, Oracle Database System (Oracle) 9
Refresh the Database• 1. Go to Blackboard and download (two)
data files from Oracle chapter6 and save under c:\oradata\chapter6\
• 2. Run the following script file– Start c:\oradata\chapter6\JLDB_Build_6.sql
Dr. Chen, Oracle Database System (Oracle) 10
Creating a Sequence (continued)
Figure 6-3 Syntax of the INSERT command
Dr. Chen, Oracle Database System (Oracle) 11
Creating a Sequence (continued)
Figure 6-4 Query USER-OBJECTS to verify existing sequence
Dr. Chen, Oracle Database System (Oracle) 12
Creating a Sequence (continued)
• To verify the settings for options of a sequence, query USER_SEQUENCES data dictionary view
Next Number to issueFigure 6-5 Verifying sequence option settings
SELECT SEQUENCE_NAME FROM USER_SEQUENCES;
SEQUENCE_NAME------------------------------ORDERS_ORDER#_SEQ
Dr. Chen, Oracle Database System (Oracle) 13
Using Sequence Values
• NEXTVAL – generates integer
Figure 6-6 Inserting a row, using a sequence to provide a PRIMARY KEY value
Dr. Chen, Oracle Database System (Oracle) 14
Using Sequence Values (continued)
Figure 6-7 Order added, using a sequence value for the Order#
Dr. Chen, Oracle Database System (Oracle) 15
Using Sequence Values (continued)
• CURRVAL – contains last integer generated by NEXTVAL
Figure 6-8 Using CURRVAL to insert an order detail row
cpk
INSERT INTO orderitems (order#, item#, isbn, quantity, paideach)VALUES (orders_order#_seq.CURRVAL, 1, 8117949391, 1, 8.50);
Dr. Chen, Oracle Database System (Oracle) 16
Using Sequence Values (continued)
Figure 6-9 Verify the CURRVAL value
Dr. Chen, Oracle Database System (Oracle) 17
Altering Sequence Definitions
• Use ALTER SEQUENCE command to change the settings for a sequence
• START WITH value cannot be altered – drop the sequence and re-create it
• Changes cannot make current integers invalid
Dr. Chen, Oracle Database System (Oracle) 18
ALTER SEQUENCE Command Example
Figure 6-11 Command to change the INCREMENT BY setting for a sequence
Dr. Chen, Oracle Database System (Oracle) 19
Checking Values on Sequences and SYSDATE
Figure 6-12 New setting for the ORDERS_ORDER#_SEQ sequence
Figure 6-13 Using the DUAL table
Dr. Chen, Oracle Database System (Oracle) 20
Checking Values on Sequences
Figure 6-14 Testing sequence values with the DUAL table Why
1041?
Dr. Chen, Oracle Database System (Oracle) 21
Removing a Sequence
• Use the DROP SEQUENCE command to delete a sequence
• Previous values generated are not affected by removing a sequence from a database
Figure 6-16 Dropping the ORDERS_ORDER#_SEQ sequence
Dr. Chen, Oracle Database System (Oracle) 22
Removing a Sequence (continued)
Figure 6-17 Verify that the sequence is removed
Dr. Chen, Oracle Database System (Oracle) 23
Indexes –Query Optimization
• If database query activity (e.g., process speed) is the priority– Indexes should be considered
• If database operations involve more DML actions than query actions– Index creation should be minimized
• An index stores frequently referenced values and ROWIDs
• Can be based on one column, multiple columns, functions, or expressions
Dr. Chen, Oracle Database System (Oracle) 24
B-Tree Index
Figure 6-19 B-tree index organization
Dr. Chen, Oracle Database System (Oracle) 25
B-Tree Index (continued)• Implicitly create an index by PRIMARY
KEY and UNIQUE constraints• Explicitly create an index by using the
CREATE INDEX command
For example:SELECT index_name FROM user_indexes;-- result on the next slide
Dr. Chen, Oracle Database System (Oracle) 26
Examples on Query Optimization
• Note that the following slides are not in the text.
• Please study them thoroughly and practice all examples (SQL commands are available in the ‘Ch6Queries.sql’.
Dr. Chen, Oracle Database System (Oracle) 27
INDEX_NAME------------------------------ACCTBONUS_AMID_PKBOOKAUTHOR_PKORDERITEMS_PKBOOKS_ISBN_PKBOOKS_COST_IDXAUTHOR_AUTHORID_PKPUBLISHER_PUBID_PKORDERS_ORDER#_PKCUSTOMERS_ZIP_DESC_IDXCUSTOMERS_ZIP_IDXCUSTOMERS_CUSTOMER#_PKEMPLOYEES_EMPNO_PKPT_CHARG_PATIENTNO_ITEMCODE_PKITEM_ITEM_CODE_PKROOM_ROOM_NO_PKACCOMODATION_ACCOM_ID_PKDOCTOR_PHYSCIAN_ID__PKPATIENT_PATIENT_NO_PKLOCATION_LOC_ID_PK
INDEX_NAME------------------------------ENROLLMENT_PKCOURSE_SECTION_CSEC_ID_PKCOURSE_COURSE_ID_PKTERM_TERM_ID_PKSTUDENT_S_ID_PKSYS_IL0000110103C00010$$FACULTY_F_ID_PKPUBLISHER3_PUBID_PKPUBLISHER2_PUBID_PKREPCONTRACTS_PKBOOKSTORES_ID_PKBOOKSTORES_NAME_UKSTOREREPS_ID_PK
32 rows selected.
For example:SELECT index_name FROM user_indexes;
What specific information is displayed on the output?Answer: _____Since they are all implicitly indexed.
Dr. Chen, Oracle Database System (Oracle) 28
Implicitly Index (cont.)
-- enter in SQL DEVELOPERSELECT table_name, index_name, index_typeFROM user_indexes;
Dr. Chen, Oracle Database System (Oracle) 29
Optimizing Query Processing -A Quick Way to Speed Access to Your data
• Indexes may be used to improve the efficiency of data searches to meet particular search criteria after the table has been in use for some time. Therefore, the ability to create indexes quickly and efficiently at any time is important.
• SQL indexes can be created on the basis of any selected attributes
Dr. Chen, Oracle Database System (Oracle) 30
BOOKS
ISBN Title PubDate PubID Cost Retail Discount CategoryVARCHAR2(10) VARCHAR2(30) DATE NUMBER(2) NUMBER(5,2) NUMBER(5,2) NUMBER(4,2) VARCHAR2(12)
BOOKS
Optimizing Query Processing – an example (not in the text)
Dr. Chen, Oracle Database System (Oracle) 31
-- chapter 6, (about the same as Figure 6-30; p. 199 )-- 'BOOKS' must be in upper caseSELECT table_name, index_name, index_typeFROM user_indexesWHERE table_name = 'BOOKS';
ISBN TITLE COST CATEGORY---------- ------------------------------ ---------- ------------4981341710 BUILDING A CAR WITH TOOTHPICKS 37.8 CHILDREN8843172113 DATABASE IMPLEMENTATION 31.4 COMPUTER3957136468 HOLY GRAIL OF ORACLE 47.25 COMPUTER1915762492 HANDCRANKED COMPUTERS 21.8 COMPUTER9959789321 E-BUSINESS THE EASY WAY 37.9 COMPUTER2491748320 PAINLESS CHILD-REARING 48 FAMILY LIFE2147428890 SHORTEST POEMS 21.85 LITERATURE
7 rows selected.
SELECT isbn, title, cost, categoryFROM booksWHERE cost > 20;
Optimizing Query Processing
Dr. Chen, Oracle Database System (Oracle) 32
Optimizing Query Processing (conti.)
Syntax:
CREATE INDEX name_of_indexON table_name (field_to_be_indexed);
For example (but, do not enter the SQL command now):CREATE INDEX books_cost_idxON books (cost);
Note that this statement defines an index called books_cost_idx for the cost column in the books table. This index ensures that in the next example SQL only needs to look at row in the database that satisfy the WHERE condition, and is, therefore, quicker to produce an answer.
Dr. Chen, Oracle Database System (Oracle) 33
Optimizing Query Processing (conti.)
Type the following SQL:SELECT isbn, title, cost, categoryFROM booksWHERE cost > 20;
ISBN TITLE COST CATEGORY---------- ------------------------------ ---------- ------------4981341710 BUILDING A CAR WITH TOOTHPICKS 37.8 CHILDREN8843172113 DATABASE IMPLEMENTATION 31.4 COMPUTER3957136468 HOLY GRAIL OF ORACLE 47.25 COMPUTER1915762492 HANDCRANKED COMPUTERS 21.8 COMPUTER9959789321 E-BUSINESS THE EASY WAY 37.9 COMPUTER2491748320 PAINLESS CHILD-REARING 48 FAMILY LIFE2147428890 SHORTEST POEMS 21.85 LITERATURE
7 rows selected.
CREATE INDEX books_cost_idx ON books (cost); SQL> CREATE INDEX books_cost_idx ON books (cost);
Index created.
Dr. Chen, Oracle Database System (Oracle) 34
Optimizing Query Processing (conti.)
SELECT isbn, title, cost, categoryFROM booksWHERE cost > 20;ISBN TITLE COST CATEGORY---------- ------------------------------ ---------- ------------1915762492 HANDCRANKED COMPUTERS 21.8 COMPUTER2147428890 SHORTEST POEMS 21.85 LITERATURE8843172113 DATABASE IMPLEMENTATION 31.4 COMPUTER4981341710 BUILDING A CAR WITH TOOTHPICKS 37.8 CHILDREN9959789321 E-BUSINESS THE EASY WAY 37.9 COMPUTER3957136468 HOLY GRAIL OF ORACLE 47.25 COMPUTER2491748320 PAINLESS CHILD-REARING 48 FAMILY LIFE
7 rows selected.
What is the difference on the output between these two versions?
Dr. Chen, Oracle Database System (Oracle) 35
Before “INDEX”.ISBN TITLE COST CATEGORY---------- ------------------------------ ---------- ------------4981341710 BUILDING A CAR WITH TOOTHPICKS 37.8 CHILDREN8843172113 DATABASE IMPLEMENTATION 31.4 COMPUTER3957136468 HOLY GRAIL OF ORACLE 47.25 COMPUTER1915762492 HANDCRANKED COMPUTERS 21.8 COMPUTER9959789321 E-BUSINESS THE EASY WAY 37.9 COMPUTER2491748320 PAINLESS CHILD-REARING 48 FAMILY LIFE2147428890 SHORTEST POEMS 21.85 LITERATURE
7 rows selected.
After “INDEX”.ISBN TITLE COST CATEGORY---------- ------------------------------ ---------- ------------1915762492 HANDCRANKED COMPUTERS 21.8 COMPUTER2147428890 SHORTEST POEMS 21.85 LITERATURE8843172113 DATABASE IMPLEMENTATION 31.4 COMPUTER4981341710 BUILDING A CAR WITH TOOTHPICKS 37.8 CHILDREN9959789321 E-BUSINESS THE EASY WAY 37.9 COMPUTER3957136468 HOLY GRAIL OF ORACLE 47.25 COMPUTER2491748320 PAINLESS CHILD-REARING 48 FAMILY LIFE
7 rows selected.
Dr. Chen, Oracle Database System (Oracle) 36
SELECT table_name, index_name, index_typeFROM user_indexesWHERE table_name = 'BOOKS';
Index on Query Optimization
Dr. Chen, Oracle Database System (Oracle) 37
Index on Query Optimization (conti.)
-- default is ‘ASCENDING’CREATE INDEX books_cost_desc_idxON books (cost DESC);
SELECT isbn, title, cost, categoryFROM booksWHERE cost > 20;ISBN TITLE COST CATEGORY---------- ------------------------------ ---------- ------------1915762492 HANDCRANKED COMPUTERS 21.8 COMPUTER2147428890 SHORTEST POEMS 21.85 LITERATURE8843172113 DATABASE IMPLEMENTATION 31.4 COMPUTER4981341710 BUILDING A CAR WITH TOOTHPICKS 37.8 CHILDREN9959789321 E-BUSINESS THE EASY WAY 37.9 COMPUTER3957136468 HOLY GRAIL OF ORACLE 47.25 COMPUTER2491748320 PAINLESS CHILD-REARING 48 FAMILY LIFE
7 rows selected.
Why the output is still displayed as “ascending” order?
Internally, the books table has been indexed as ‘______’ order (using pointer); however, the display is on the ‘_________’ (default) order.
Dr. Chen, Oracle Database System (Oracle) 38
Index on Query Optimization (conti.)
-- chapter 6, (about the same as Figure 6-30; p. 199 )-- 'BOOKS' must be in upper caseSELECT table_name, index_name, index_typeFROM user_indexesWHERE table_name = 'BOOKS';
Dr. Chen, Oracle Database System (Oracle) 39
Query Optimization: DROP INDEX
DROP INDEX books_cost_idx; DROP INDEX books_cost_desc_idx;
-- chapter 6, (about the same as Figure 6-30; p. 199 )-- 'BOOKS' must be in upper caseSELECT table_name, index_name, index_typeFROM user_indexesWHERE table_name = 'BOOKS';
Dr. Chen, Oracle Database System (Oracle) 40
Summary on Optimizing Query Processing (cont.)
hThe indexes are defined so as to optimize the processing of SELECT statements. ;
hAn index is never explicitly referenced in a SELECT statement; the syntax of SQL does not allow this;
hDuring the processing of a statement, SQL itself determines whether an existing index will be used;
hAn index may be created or deleted at any time;hWhen updating, inserting or deleting rows, SQL also
maintains the indexes on the tables concerned. This means that, on the one hand, the processing time for SELECT statements is reduced, while, on the other hand, the processing time for update statements (such as INSERT, UPDATE and DELETE) can increase.
Dr. Chen, Oracle Database System (Oracle) 41
Your Turn …• Practice the following examples (from the
text)
Dr. Chen, Oracle Database System (Oracle) 42
CREATE INDEX Command Examples
Figure 6-18 Creating an index on the Zip column
Dr. Chen, Oracle Database System (Oracle) 43
The Explain Plan
Figure 6-20 View the explain plan indicating a full table scan
Dr. Chen, Oracle Database System (Oracle) 44
The Explain Plan (continued)
Figure 6-21 View the explain plan indicating a full table scan
Dr. Chen, Oracle Database System (Oracle) 45
UNIQUE INDEX
Figure 6-22 Explicitly creating a unique index
-- chapter 6, Figure 6-23; p. 195CREATE INDEX customers_zip_desc_idx ON customers (zip DESC);
Dr. Chen, Oracle Database System (Oracle) 46
CREATE INDEX Command Examples
Figure 6-24 Creating a composite index
• The composite index could improve the performance of queries that include a search condition on both the Lastname and Firstname column. • Generally, it is more efficient than creating two separate
single-column indexes because less I/O is required to read a single index.
Dr. Chen, Oracle Database System (Oracle) 47
Verifying Composite Index
SELECT customer#, lastname, firstname, city, state, zipFROM customers;
-- chapter 6, Figure 6-24; p. 195CREATE INDEX customer_name_idxON customers (lastname, firstname);
SELECT customer#, lastname, firstname, city, state, zipFROM customers;
After tested, no significant performance can be found since it is a very small database.
Any performance improvement?
Dr. Chen, Oracle Database System (Oracle) 48
• Practice all the examples in the text.• A Script file is available on the Bb (file
name: Ch6Queries.sql)• After completing all examples, do the HW.
Dr. Chen, Oracle Database System (Oracle) 49
Homework - Hands-On Assignments
Read and Practice all examples on Chapters 6• 1. Run the script files (in the folder \oradata\
chapter5\): JLDB_Build_6.sql• 2. Read Oracle assignment and create a script file
Oracle_ch6_Lname_Fname.sql for questions (#1 to #5 and #9; pp.211-212) on “Hands-on Assignments”. Use appropriate COLUMN statements to produce readable outputs if needed.
• 3. Execute and test one problem at a time and make sure they are all running successfully.
• 4. When you done, spool the script files (see next slide for spooling instructions) and UPLOAD the spooled file (Oracle_ch6_Spool_Lname_Fname.txt) to Bb by the deadline .
Upload the spooled file (*.txt) to the Bb (under “Assignments & Projects”) by the deadline.
Dr. Chen, Oracle Database System (Oracle) 50
How to Spool your Script and Output Files
After you tested the script file of Oracle_ch6_Lname_Fname.sql successfully, follow the instructions below to spool both script and output files:
Step 0. Run the following script file from SQL*Plus (since you have created JLDB tables)– Start c:\oradata\chapter6\JLDB_Build_6.sql
• 1. type the following on SQL>– Spool c:\oradata\Oracle_ch6_Spool_Lname_Fname.txt (make sure your name is entered)
• 2. open Oracle_ch6_Lname_Fname.sql that you already tested• 3. copy and paste all the SQL commands (including all comments) to the
SQL*PLUS • 4. type Spool Off on the SQL>The output should contain your personal information, all SQL commands and
their solution on the .txt file and saved in C: drive (oradata\ folder)
Dr. Chen, Oracle Database System (Oracle) 51
Summary
• A sequence can be created to generate a series of integers• The values generated by a sequence can be stored in any table• A sequence is created with the CREATE SEQUENCE command• Gaps in sequences might occur if the values are stored in various
tables, if numbers are cached but not used, or if a rollback occurs• A value is generated by using the NEXTVAL pseudocolumn• The CURRVAL pseudocolumn is NULL until a value is generated
by NEXTVAL• The USER_OBJECTS data dictionary object can be used to
confirm the existence of all schema objects• The USER_SEQUENCES data dictionary object is used to view
sequence settings
Dr. Chen, Oracle Database System (Oracle) 52
Summary (continued)• The ALTER SEQUENCE command is used to modify an existing
sequence; the only settings that can’t be modified are the START WITH option and any option that would be invalid because of previously generated values
• The DUAL table is helpful for testing sequence value generation• The DROP SEQUENCE command deletes an existing sequence• An index can be created to speed up the query process• DML operations are always slower when indexes exist• Oracle 11g creates an index for PRIMARY KEY and UNIQUE
constraints automatically• An explicit index is created with the CREATE INDEX command• An index can be used by Oracle 11g automatically if a query
criterion or sort operation is based on a column or an expression used to create the index
Dr. Chen, Oracle Database System (Oracle) 53
Summary (continued)
• The two main structures for indexes are B-tree and bitmap• The explain plan can verify whether an index is used in a
query• Function-based indexes are used to index an expression or
the use of functions on a column or columns• An index organized table is a table stored in a B-tree
structure to combine the index and table into one database object
• Information about an index can be retrieved from the USER_INDEXES and USER_IND_COLUMNS views
• An index can be dropped with the DROP INDEX command• An index can be renamed with the ALTER INDEX command
Dr. Chen, Oracle Database System (Oracle) 54
Summary (continued)
• Except for a name change, an index can’t be modified; it must be deleted and then re-created
• A synonym provides a permanent alias for a database object• A public synonym is available to any database user• A private synonym is available only to the user who created
it• A synonym is created by using the CREATE SYNONYM
command• A synonym is deleted by using the DROP SYNONYM
command• Only a user with DBA privileges can drop a public synonym
Dr. Chen, Oracle Database System (Oracle) 55
END OF CHAPTER 6