CREATE INDEX
SQL - Language Statements
CREATE INDEX
Constructs a secondary index
1998-09-09
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( column [, ... ]) ops_name )
1998-09-09
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.
1998-09-09
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.
1998-09-09
Description
CREATE INDEX constructs an index
index_name.
on the specified
table.
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.
1998-09-09
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
1998-09-09
SQL92
CREATE INDEX is a Postgres language extension.
There is no CREATE INDEX command in SQL92.