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-.pgaw:Help.f.t insert end "CREATE INDEX" {bold} " 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.
-
-" {} "Synopsis" {bold} "
-
-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 )
-
-" {code} "Inputs" {bold} "
-
-" {} "UNIQUE" {italic} "
- 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" {italic} "
- The name of the index to be created.
-
-" {} "table" {italic} "
- The name of the table to be indexed.
-
-" {} "acc_name" {italic} "
- 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" {italic} "
- The name of a column of the table.
-
-" {} "ops_name" {italic} "
- 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
-
-" {code} "func_name" {italic} "
- A user-defined function, which returns a value that can be indexed.
-
-" {} "Outputs" {bold} "
-
-" {} "CREATE" {italic} "
- The message returned if the index is successfully created.
-
-" {} "ERROR: Cannot create index: 'index_name' already exists." {italic} "
- This error occurs if it is impossible to create the index.
-
-" {} "Usage" {bold} "
-
-To create a btree index on the field title in the table films:
-" {} "
-CREATE UNIQUE INDEX title_idx
- ON films (title);
-
-" {code} "Notes" {bold} "
-
-Currently, only the BTREE access method supports multi-column indexes. Up to 7 keys may be specified.
-
-Use DROP INDEX to remove an index. "