This page in other versions: Unsupported versions: 6.4 / 6.5 / 7.0

CREATE INDEX

Name

CREATE INDEX — Constructs a secondary index
CREATE [ UNIQUE ] INDEX index_name
    ON table [ USING acc_name ]
    ( column [ ops_name] [, ...] )
CREATE [ UNIQUE ] INDEX index_name
    ON table [ USING acc_name ]
    ( func_name( r">colle> [, ... ]) ops_name )
  

Inputs

UNIQUE

Causes the system to check for duplicate values in the table when the index is created (if data already exist) and each time data is added. Attempts to insert or update non-duplicate data will generate an error.

index_name

The name of the index to be created.

table

The name of the table to be indexed.

acc_name

the name of the access method which is to be used for the index. The default access method is BTREE. Postgres provides three access methods for secondary indexes:

BTREE

an implementation of the Lehman-Yao high-concurrency btrees.

RTREE

implements standard rtrees using Guttman's quadratic split algorithm.

HASH

an implementation of Litwin's linear hashing.

column

The name of a column of the table.

ops_name

An associated operator class. The following select list returns all ops_names:

SELECT am.amname AS acc_name,
       opc.opcname AS ops_name,
       opr.oprname AS ops_comp
    FROM pg_am am, pg_amop amop,
         pg_opclass opc, pg_operator opr
    WHERE amop.amopid = am.oid AND
          amop.amopclaid = opc.oid AND
          amop.amopopr = opr.oid
    ORDER BY acc_name, ops_name, ops_comp
        
func_name

A user-defined function, which returns a value that can be indexed.

Outputs

CREATE

The message returned if the index is successfully created.

ERROR: Cannot create index: 'index_name' already exists.

This error occurs if it is impossible to create the index.

Description

CREATE INDEX constructs an index index_name. on the specified table.

Tip: Indexes are primarily used to enhance database performance. But inappropriate use will result in slower performance.

In the first syntax shown above, the key fields for the index are specified as column names; a column may also have an associated operator class. An operator class is used to specify the operators to be used for a particular index. For example, a btree index on four-byte integers would use the int4_ops class; this operator class includes comparison functions for four-byte integers. The default operator class is the appropriate operator class for that field type.

In the second syntax, an index is defined on the result of a user-defined function func_name applied to one or more attributes of a single class. These functional indexes can be used to obtain fast access to data based on operators that would normally require some transformation to apply them to the base data.

Notes

Currently, only the BTREE access method supports multi-column indexes. Up to 7 keys may be specified.

Use DROP INDEX to remove an index.

Usage

To create a btree index on the field title in the table films:

CREATE UNIQUE INDEX title_idx
    ON films (title);
  

Compatibility

SQL92

CREATE INDEX is a Postgres language extension.

There is no CREATE INDEX command in SQL92.

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group