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 )
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.
The name of the index to be created.
The name of the table to be indexed.
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:
an implementation of the Lehman-Yao high-concurrency btrees.
implements standard rtrees using Guttman's quadratic split algorithm.
an implementation of Litwin's linear hashing.
The name of a column of the table.
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
A user-defined function, which returns a value that can be indexed.
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.
To create a btree index on the field title in the table films:
CREATE UNIQUE INDEX title_idx ON films (title);