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Oracle Tutorials - Indexes for the PRIMARY KEY Column

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(Continued from previous topic...)

What Is an Index Associated with a Constraint?

An index associated with a constraint because this constraint is required to have an index. There are two types of constraints are required to have indexes: UNIQUE and PRIMARY KEY. When you defines a UNIQUE or PRIMARY KEY constraint in a table, Oracle will automatically create an index for that constraint. The following script shows you an example:

CREATE TABLE student (id NUMBER(5) PRIMARY KEY,
  first_name VARCHAR(80) NOT NULL,
  last_name VARCHAR(80) NOT NULL,
  birth_date DATE NOT NULL,
  social_number VARCHAR(80) UNIQUE NOT NULL);
Table created.
  
SELECT index_name, table_name, uniqueness 
  FROM USER_INDEXES WHERE table_name = 'STUDENT';
INDEX_NAME              TABLE_NAME            UNIQUENES
----------------------- --------------------- ---------
SYS_C004123             STUDENT               UNIQUE
SYS_C004124             STUDENT               UNIQUE

The result confirms that Oracle automatically created two indexes for you.

(Continued on next topic...)

1. What Is an Index?
2. How To Run SQL Statements through the Web Interface?
3. How To Create a Table Index?
4. How To List All Indexes in Your Schema?
5. What Is an Index Associated with a Constraint?
6. How To Rename an Index?
7. How To Drop an Index?
8. Can You Drop an Index Associated with a Unique or Primary Key Constraint?
9. What Happens to Indexes If You Drop a Table?
10. How To Recover a Dropped Index?
11. What Happens to the Indexes If a Table Is Recovered?
12. How To Rebuild an Index?
13. How To See the Table Columns Used in an Index?
14. How To Create a Single Index for Multiple Columns?