Chapter 12 Additional Database Objects

Chapter Objectives  Define the purpose of a sequence and state how it can be used by an organization  Explain why gaps may appear in the integers generated by a sequence  Correctly use the CREATE SEQUENCE command to create a sequence  Define the purpose of a sequence and state how it can be used by an organization  Explain why gaps may appear in the integers generated by a sequence  Correctly use the CREATE SEQUENCE command to create a sequence

Chapter Objectives  Identify which options cannot be changed by the ALTER SEQUENCE command  Use NEXTVAL and CURRVAL in an INSERT command  Explain when Oracle9i will automatically create an index  Create an index, using the CREATE INDEX command  Identify which options cannot be changed by the ALTER SEQUENCE command  Use NEXTVAL and CURRVAL in an INSERT command  Explain when Oracle9i will automatically create an index  Create an index, using the CREATE INDEX command

Chapter Objectives  Delete an index, using the DELETE INDEX command  Create a PUBLIC synonym  Delete a PUBLIC synonym  Identify the contents of different versions of views used to access the data dictionary, based on the prefix of the view  Delete an index, using the DELETE INDEX command  Create a PUBLIC synonym  Delete a PUBLIC synonym  Identify the contents of different versions of views used to access the data dictionary, based on the prefix of the view

Database Objects  Anything that has a name and defined structure  Includes: –Sequence – generate sequential integers –Index – quickly locate specific records –Synonym – alias for other database objects  Anything that has a name and defined structure  Includes: –Sequence – generate sequential integers –Index – quickly locate specific records –Synonym – alias for other database objects

Sequences  Used for internal control purposes by providing sequential integers for auditing  Used to generate unique value for primary key column – no correlation with actual row contents  Used for internal control purposes by providing sequential integers for auditing  Used to generate unique value for primary key column – no correlation with actual row contents

CREATE SEQUENCE Command  Various intervals allowed – Default: 1  Can specify starting number – Default: 1  Various intervals allowed – Default: 1  Can specify starting number – Default: 1

CREATE SEQUENCE Command  Can specify MINVALUE for decreasing sequence, MAXVALUE for increasing  Numbers can be reused if CYCLE specified  ORDER clause for application cluster environment  Use CACHE to pre-generate integers – Default: 20  Can specify MINVALUE for decreasing sequence, MAXVALUE for increasing  Numbers can be reused if CYCLE specified  ORDER clause for application cluster environment  Use CACHE to pre-generate integers – Default: 20

CREATE SEQUENCE Command Example

Verifying Sequence Values Query USER_SEQUENCES data dictionary view

Using Sequence Values  NEXTVAL – generates integer  CURRVAL – contains last integer generated by NEXTVAL  NEXTVAL – generates integer  CURRVAL – contains last integer generated by NEXTVAL

Altering Sequence Definitions  Use ALTER SEQUENCE command  START WITH value cannot be altered – drop sequence and re-create  Changes cannot make current integers invalid  Use ALTER SEQUENCE command  START WITH value cannot be altered – drop sequence and re-create  Changes cannot make current integers invalid

ALTER SEQUENCE Command Example

DROP SEQUENCE Command Previous values generated are not affected by removing a sequence from a database

Indexes  Stores frequently referenced value and row ID (ROWID)  Can be based on one column, multiple columns, functions, or expressions  Stores frequently referenced value and row ID (ROWID)  Can be based on one column, multiple columns, functions, or expressions

Creating an Index  Implicitly created by PRIMARY KEY and UNIQUE constraints  Explicitly created by CREATE INDEX command  Implicitly created by PRIMARY KEY and UNIQUE constraints  Explicitly created by CREATE INDEX command

CREATE INDEX Command Example

Verifying an Index Indexes listed in USER_INDEXES view

Removing an Index Use DROP INDEX command

Synonyms  Serve as permanent aliases for database objects  Can be private or public –Private synonyms are only available to user who created them –PUBLIC synonyms are available to all database users  Serve as permanent aliases for database objects  Can be private or public –Private synonyms are only available to user who created them –PUBLIC synonyms are available to all database users

CREATE SYNONYM Command Syntax

CREATE SYNONYM Command Example

Deleting a SYNONYM  A private synonym can be deleted by owner  A PUBLIC synonym can only be deleted by a user with DBA privileges  A private synonym can be deleted by owner  A PUBLIC synonym can only be deleted by a user with DBA privileges

Data Dictionary  Stores information about database objects  Owned by user SYS  Cannot be directly accessed by users  Displays contents through data dictionary views  Stores information about database objects  Owned by user SYS  Cannot be directly accessed by users  Displays contents through data dictionary views

View Prefixes