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ALTER INDEX
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ALTER INDEX

ALTER INDEX — change the definition of an index

Synopsis

ALTER INDEX [ IF EXISTS ]name RENAME TOnew_nameALTER INDEX [ IF EXISTS ]name SET TABLESPACEtablespace_nameALTER INDEXname ATTACH PARTITIONindex_nameALTER INDEXname [ NO ] DEPENDS ON EXTENSIONextension_nameALTER INDEX [ IF EXISTS ]name SET (storage_parameter [=value] [, ... ] )ALTER INDEX [ IF EXISTS ]name RESET (storage_parameter [, ... ] )ALTER INDEX [ IF EXISTS ]name ALTER [ COLUMN ]column_number    SET STATISTICSintegerALTER INDEX ALL IN TABLESPACEname [ OWNED BYrole_name [, ... ] ]    SET TABLESPACEnew_tablespace [ NOWAIT ]

Description

ALTER INDEX changes the definition of an existing index. There are several subforms described below. Note that the lock level required may differ for each subform. AnACCESS EXCLUSIVE lock is held unless explicitly noted. When multiple subcommands are listed, the lock held will be the strictest one required from any subcommand.

RENAME

TheRENAME form changes the name of the index. If the index is associated with a table constraint (eitherUNIQUE,PRIMARY KEY, orEXCLUDE), the constraint is renamed as well. There is no effect on the stored data.

Renaming an index acquires aSHARE UPDATE EXCLUSIVE lock.

SET TABLESPACE

This form changes the index's tablespace to the specified tablespace and moves the data file(s) associated with the index to the new tablespace. To change the tablespace of an index, you must own the index and haveCREATE privilege on the new tablespace. All indexes in the current database in a tablespace can be moved by using theALL IN TABLESPACE form, which will lock all indexes to be moved and then move each one. This form also supportsOWNED BY, which will only move indexes owned by the roles specified. If theNOWAIT option is specified then the command will fail if it is unable to acquire all of the locks required immediately. Note that system catalogs will not be moved by this command, useALTER DATABASE or explicitALTER INDEX invocations instead if desired. See alsoCREATE TABLESPACE.

ATTACH PARTITIONindex_name

Causes the named index (possibly schema-qualified) to become attached to the altered index. The named index must be on a partition of the table containing the index being altered, and have an equivalent definition. An attached index cannot be dropped by itself, and will automatically be dropped if its parent index is dropped.

DEPENDS ON EXTENSIONextension_name NO DEPENDS ON EXTENSIONextension_name

This form marks the index as dependent on the extension, or no longer dependent on that extension ifNO is specified. An index that's marked as dependent on an extension is automatically dropped when the extension is dropped.

SET (storage_parameter [=value] [, ... ] )

This form changes one or more index-method-specific storage parameters for the index. SeeCREATE INDEX for details on the available parameters. Note that the index contents will not be modified immediately by this command; depending on the parameter you might need to rebuild the index withREINDEX to get the desired effects.

RESET (storage_parameter [, ... ] )

This form resets one or more index-method-specific storage parameters to their defaults. As withSET, aREINDEX might be needed to update the index entirely.

ALTER [ COLUMN ]column_number SET STATISTICSinteger

This form sets the per-column statistics-gathering target for subsequentANALYZE operations, though can be used only on index columns that are defined as an expression. Since expressions lack a unique name, we refer to them using the ordinal number of the index column. The target can be set in the range 0 to 10000; alternatively, set it to -1 to revert to using the system default statistics target (default_statistics_target). For more information on the use of statistics by thePostgres Pro query planner, refer toSection 14.2.

Parameters

IF EXISTS: Do not throw an error if the index does not exist. A notice is issued in this case.
column_number: The ordinal number refers to the ordinal (left-to-right) position of the index column.
name: The name (possibly schema-qualified) of an existing index to alter.
new_name: The new name for the index.
tablespace_name: The tablespace to which the index will be moved.
extension_name: The name of the extension that the index is to depend on.
storage_parameter: The name of an index-method-specific storage parameter.
value: The new value for an index-method-specific storage parameter. This might be a number or a word depending on the parameter.

Notes

These operations are also possible usingALTER TABLE.ALTER INDEX is in fact just an alias for the forms ofALTER TABLE that apply to indexes.

There was formerly anALTER INDEX OWNER variant, but this is now ignored (with a warning). An index cannot have an owner different from its table's owner. Changing the table's owner automatically changes the index as well.

Changing any part of a system catalog index is not permitted.

Examples

To rename an existing index:

ALTER INDEX distributors RENAME TO suppliers;

To move an index to a different tablespace:

ALTER INDEX distributors SET TABLESPACE fasttablespace;

To change an index's fill factor (assuming that the index method supports it):

ALTER INDEX distributors SET (fillfactor = 75);REINDEX INDEX distributors;

Set the statistics-gathering target for an expression index:

CREATE INDEX coord_idx ON measured (x, y, (z + t));ALTER INDEX coord_idx ALTER COLUMN 3 SET STATISTICS 1000;

Compatibility

ALTER INDEX is aPostgres Pro extension.