SQL CREATE INDEX Statement

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.

CREATE INDEX Syntax

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

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:

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

CREATE INDEX Example

The SQL statement below creates an index named “idx_lastname” on the “LastName” column in the “Persons” table:

CREATE INDEX idx_lastname
ON Persons (LastName); 

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

CREATE INDEX idx_pname
ON Persons (LastName, FirstName); 

DROP INDEX Statement

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

MS Access:

DROP INDEX index_name ON table_name; 

SQL Server:

DROP INDEX table_name.index_name; 

DB2/Oracle:

DROP INDEX index_name; 

MySQL:

ALTER TABLE table_name
DROP INDEX index_name;