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Oracle Tutorials - Indexes for the PRIMARY KEY Column
(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);
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...)
- What Is an Index?
- How To Run SQL Statements through the Web Interface?
- How To Create a Table Index?
- How To List All Indexes in Your Schema?
- What Is an Index Associated with a Constraint?
- How To Rename an Index?
- How To Drop an Index?
- Can You Drop an Index Associated with a Unique or Primary Key Constraint?
- What Happens to Indexes If You Drop a Table?
- How To Recover a Dropped Index?
- What Happens to the Indexes If a Table Is Recovered?
- How To Rebuild an Index?
- How To See the Table Columns Used in an Index?
- How To Create a Single Index for Multiple Columns?