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 [ NO ] 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.
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 extension_name
NO DEPENDS ON EXTENSION extension_name
This form marks the index as dependent on the extension,
or no longer dependent on that extension if NO 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. See CREATE 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 with REINDEX 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 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 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.
