SQL CREATE INDEX Statement

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# SQL CREATE INDEX Statement

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

Indexes allow the database application to find data fast; without reading the whole table.

## Indexes

An index can be created in a table to find data more quickly and efficiently.

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 you should only create indexes on columns (and tables) that will be frequently searched against.

### SQL CREATE INDEX Syntax

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

    CREATE INDEX index_name
    ON table_name (column_name)

### SQL CREATE UNIQUE INDEX Syntax

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

    CREATE UNIQUE INDEX index_name
    ON table_name (column_name)

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

## CREATE INDEX Example

The SQL statement below creates an index named "PIndex" on the "LastName" column in the "Persons" table:

    CREATE INDEX PIndex
    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 PIndex
    ON Persons (LastName, FirstName)

From http://www.w3schools.com (Copyright Refsnes Data)