NAME

       ALTER_INDEX - change the definition of an index

SYNOPSIS

       ALTER INDEX [ IF EXISTS ] name RENAME TO new_name
       ALTER INDEX [ IF EXISTS ] name SET TABLESPACE tablespace_name
       ALTER INDEX name ATTACH PARTITION index_name
       ALTER INDEX name DEPENDS ON EXTENSION extension_name
       ALTER 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 STATISTICS integer
       ALTER INDEX ALL IN TABLESPACE name [ OWNED BY role_name [, ... ] ]
           SET TABLESPACE new_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. An ACCESS
       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
           The RENAME form changes the name of the index. If the index is associated with a table
           constraint (either UNIQUE, PRIMARY KEY, or EXCLUDE), the constraint is renamed as
           well. There is no effect on the stored data.

           Renaming an index acquires a SHARE 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 have CREATE privilege on the new tablespace.
           All indexes in the current database in a tablespace can be moved by using the ALL IN
           TABLESPACE form, which will lock all indexes to be moved and then move each one. This
           form also supports OWNED BY, which will only move indexes owned by the roles
           specified. If the NOWAIT 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, use ALTER DATABASE or explicit ALTER INDEX
           invocations instead if desired. See also CREATE TABLESPACE (CREATE_TABLESPACE(7)).

       ATTACH PARTITION
           Causes the named index 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 EXTENSION
           This form marks the index as dependent on the extension, such that if the extension is
           dropped, the index will automatically be dropped as well.

       SET ( storage_parameter [= value] [, ... ] )
           This form changes one or more index-method-specific storage parameters for the index.
           See CREATE INDEX (CREATE_INDEX(7)) 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 with REINDEX(7) to get the desired
           effects.

       RESET ( storage_parameter [, ... ] )
           This form resets one or more index-method-specific storage parameters to their
           defaults. As with SET, a REINDEX might be needed to update the index entirely.

       ALTER [ COLUMN ] column_number SET STATISTICS integer
           This form sets the per-column statistics-gathering target for subsequent ANALYZE(7)
           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 the
           PostgreSQL query planner, refer to Section 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 using ALTER TABLE (ALTER_TABLE(7)).  ALTER INDEX is in
       fact just an alias for the forms of ALTER TABLE that apply to indexes.

       There was formerly an ALTER 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 a PostgreSQL extension.

SEE ALSO

       CREATE INDEX (CREATE_INDEX(7)), REINDEX(7)