Tài liệu oracle data dictionary ppt

The Oracle data dictionary is one of the most important components of the Oracle7 Server.. The Oracle data dictionary is one of the most important components of the Oracle7 Server.. Tabl

Oracle Data Dictionary

10

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 10Ć2

The Oracle data dictionary is one of the most important components of the Oracle7 Server It consists of a set of tables and views that provide a read-only reference to the database.

At the end of this lesson, you should be able to

D Describe the data dictionary views a user may access

D Query data from the data dictionary

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 10Ć4

The Oracle data dictionary is one of the most important components of the Oracle7

Server It is created when a database is created Whenever the database is in

operation, the data dictionary is updated and maintained by the Oracle7 Server Alldata dictionary tables are owned by the SYS user The base tables are rarely accesseddirectly because the information in them is not easy to understand Therefore, userstypically access data dictionary views because the information is presented in aformat that is easy for them to understand

Tables Within the Oracle7 Database

Tables Description

User tables Collection of tables created and maintained by the user,

such as S_EMP, that contain user information

Data dictionary Collection of tables created and maintained by the Oracle7

Server, such as USER_OBJECTS, that contain informationabout the database

Example Data Dictionary Contents

D Names of Oracle7 Server users

D Privileges granted to users

D Database object names (for example, tables, views, and indexes)

D Table constraints

D Auditing information, such as who has accessed or updated specified databaseobjects

Data Dictionary Uses

The data dictionary is a reference for all database users It is a valuable source ofinformation for end users, application designers, and DBAs The data dictionary isalso critical for the operation of the Oracle7 Server because the database relies on thedata dictionary to record and verify information about itself

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 10Ć6

Querying the Data Dictionary

You can query the data dictionary by issuing a SQL SELECT statement Depending

on your privileges, you can query various views

View Classes

Data dictionary view names reflect their intended use There are four categories ofviews; each category has a distinct prefix

Prefix Description

USER_ Contains objects owned by the user For example, views with this prefix

allow the user to display information about tables created by the user andprivileges granted by the user

ALL_ Accesses objects to which the user has been granted access rights, in

addition to objects owned by the user

DBA_ Allows users with the DBA privilege to access any object in the

database

V$ Displays database server performance and locking Initially available

only to the DBA

Additional Views

Several data dictionary views do not use the prefixes listed above These includesynonyms for views with long names

View Name Description

DICTIONARY Lists all data dictionary tables, views, and synonyms.TABLE_PRIVILEGES Grants on objects for which the user is the grantor,

grantee, or owner

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 10Ć8

Querying the Data Dictionary continued

Example

The DICTIONARY view lists all data dictionary views accessible to the user with abrief description of the object in a comment column You can also reference thesynonym for the view, DICT

-OBJECT_TYPE VARCHAR2(13)CREATED DATE

LAST_DDL_TIME DATE

TIMESTAMP VARCHAR2(75)STATUS VARCHAR2(7)

3 WHERE table_name = ’USER_OBJECTS’;

For more information, see

Oracle7 Server SQL Language Quick Reference, Release 7.3.

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 10Ć10

Querying the Data Dictionary continued

Example

Display the types of objects that the user owns

SQL> SELECT DISTINCT object_type

2 FROM user_objects;

Example

You can search the data dictionary for a specific topic by querying the COMMENTScolumn in the DICTIONARY view Find all data dictionary views pertaining to thekeyword Grant

COLUMN table_name FORMAT A20

COLUMN comments FORMAT A30

e user is the grantor, grantee , owner,

or an enabled role or PUBLIC i

s the grantee

ALL_COL_PRIVS_MADE Grants on columns for which th

e user is owner or grantor

ALL_COL_PRIVS_RECD Grants on columns for which th

e user, PUBLIC or enabled role

is the grantee

20 rows selected

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 10Ć12

Checking Constraints on a Table

After creating a table, you can confirm its existence by issuing a DESCRIBE

command The only constraint you can verify is the NOT NULL constraint To viewall constraints on your table, you can check the USER_CONSTRAINTS table.Example

Confirm the constraints on the S_EMP table

SQL> SELECT constraint_name, constraint_type,

2 search_condition, r_constraint_name

3 FROM user_constraints

4 WHERE table_name = ’S_EMP’;

CONSTRAINT_NAME C SEARCH_CONDITION R_CONSTRAINT_NA - - - - S_EMP_MANAGER_ID_FK R S_EMP_ID_PK

S_EMP_LAST_NAME_NN C LAST_NAME IS NOT NULL

S_EMP_USERID_NN C USERID IS NOT NULL

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 10Ć14

Checking Constraints on a Table continued

View the names of the columns involved in constraints by querying the

USER_CONS_COLUMNS data dictionary view This view is especially useful forconstraints that use the system-assigned name

Example

Display the column constraint information in the data dictionary for the S_EMP table

SQL> SELECT constraint_name, column_name

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 10Ć16

The data dictionary is a set of tables that the user can query through views The datadictionary holds all the data about the database Write a SELECT statement to displaythe contents of the data dictionary views

Frequently Accessed Data Dictionary Views

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 10Ć18

Practice Overview

In this practice, you will access the data dictionary views to verify information aboutyour tables

Practice Contents

D Querying the data dictionary to view table information

D Viewing constraint information from the data dictionary

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 10Ć20

Note: If you did not complete Practice 9, Exercise 2 and Exercise 3, you can invoke

scripts p9q2.sql and p9q3.sql to create DEPARTMENT table and

EMPLOYEE table respectively

3. Query the USER_OBJECTS data dictionary to see information about the tablesyou created in Practice 9, DEPARTMENT and EMPLOYEE tables

4. Create a script to execute a generic query to confirm the constraints for the tablesyou have created You can use a substitution parameter for the table name Save

the query as p10q4.sql Execute the script to confirm the constraints for the tables

you created in Practice 9, DEPARTMENT and EMPLOYEE tables

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 10Ć22