SQL CREATE INDEX Statement

The CREATE INDEX statement is used to create indexes in tables.

Indexes are used to retrieve data from the database more quickly than otherwise. The users cannot see the indexes, they are just used to speed up searches/queries.

Note: Updating a table with indexes takes more time than updating a table without (because the indexes also need an update). So, only create indexes on columns that will be frequently searched against.

CREATE INDEX Syntax

Creates an index on a table. Duplicate values are allowed:

Syntax

CREATE INDEX index_name
ON table_name(column1, column2, ....);

CREATE UNIQUE INDEX Syntax

Creates a unique index on a table. Duplicate values are not allowed:

Example

CREATE UNIQUE INDEX  index_name

ON table_name(column1, column2, ....);

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Note:The syntax for creating indexes varies among different databases. Therefore: Check the syntax for creating indexes in your database.

CREATE INDEX Example

The SQL statement below creates an index named "idx_firstname" on the "FristName" column in the "student" table:

Example

 CREATE INDEX  idx_firstname

 ON student (FirstName) ;

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If you want to create an index on a combination of columns, you can list the column names within the parentheses, separated by commas:

Example

 CREATE INDEX  idx_pname

  ON student (FirstName, LastName) ;

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DROP INDEX Statement

The DROP INDEX statement is used to delete an index in a table.

Syntax

Ms Access: 

 DROP INDEX index_name
 ON table_name ;

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Syntax

SQL Server: 

 DROP INDEX 
table_name.index_name ;

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Syntax

DB2/Oracle: 


 DROP INDEX index_name

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Syntax

MySQL: 


 ALTER TABLE table_name
 DROP INDEX index_name;

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