NAME

       ALTER_COLLATION - change the definition of a collation

SYNOPSIS

       ALTER COLLATION name REFRESH VERSION

       ALTER COLLATION name RENAME TO new_name
       ALTER COLLATION name OWNER TO { new_owner | CURRENT_ROLE | CURRENT_USER | SESSION_USER }
       ALTER COLLATION name SET SCHEMA new_schema

DESCRIPTION

       ALTER COLLATION changes the definition of a collation.

       You must own the collation to use ALTER COLLATION. To alter the owner, you must be able to SET ROLE to
       the new owning role, and that role must have CREATE privilege on the collation's schema. (These
       restrictions enforce that altering the owner doesn't do anything you couldn't do by dropping and
       recreating the collation. However, a superuser can alter ownership of any collation anyway.)

PARAMETERS

       name
           The name (optionally schema-qualified) of an existing collation.

       new_name
           The new name of the collation.

       new_owner
           The new owner of the collation.

       new_schema
           The new schema for the collation.

       REFRESH VERSION
           Update the collation's version. See Notes below.

NOTES

       When a collation object is created, the provider-specific version of the collation is recorded in the
       system catalog. When the collation is used, the current version is checked against the recorded version,
       and a warning is issued when there is a mismatch, for example:

           WARNING:  collation "xx-x-icu" has version mismatch
           DETAIL:  The collation in the database was created using version 1.2.3.4, but the operating system provides version 2.3.4.5.
           HINT:  Rebuild all objects affected by this collation and run ALTER COLLATION pg_catalog."xx-x-icu" REFRESH VERSION, or build PostgreSQL with the right library version.

       A change in collation definitions can lead to corrupt indexes and other problems because the database
       system relies on stored objects having a certain sort order. Generally, this should be avoided, but it
       can happen in legitimate circumstances, such as when upgrading the operating system to a new major
       version or when using pg_upgrade to upgrade to server binaries linked with a newer version of ICU. When
       this happens, all objects depending on the collation should be rebuilt, for example, using REINDEX. When
       that is done, the collation version can be refreshed using the command ALTER COLLATION ... REFRESH
       VERSION. This will update the system catalog to record the current collation version and will make the
       warning go away. Note that this does not actually check whether all affected objects have been rebuilt
       correctly.

       When using collations provided by libc, version information is recorded on systems using the GNU C
       library (most Linux systems), FreeBSD and Windows. When using collations provided by ICU, the version
       information is provided by the ICU library and is available on all platforms.

           Note

           When using the GNU C library for collations, the C library's version is used as a proxy for the
           collation version. Many Linux distributions change collation definitions only when upgrading the C
           library, but this approach is imperfect as maintainers are free to back-port newer collation
           definitions to older C library releases.

           When using Windows for collations, version information is only available for collations defined with
           BCP 47 language tags such as en-US.

       For the database default collation, there is an analogous command ALTER DATABASE ... REFRESH COLLATION
       VERSION.

       The following query can be used to identify all collations in the current database that need to be
       refreshed and the objects that depend on them:

           SELECT pg_describe_object(refclassid, refobjid, refobjsubid) AS "Collation",
                  pg_describe_object(classid, objid, objsubid) AS "Object"
             FROM pg_depend d JOIN pg_collation c
                  ON refclassid = 'pg_collation'::regclass AND refobjid = c.oid
             WHERE c.collversion <> pg_collation_actual_version(c.oid)
             ORDER BY 1, 2;

EXAMPLES

       To rename the collation de_DE to german:

           ALTER COLLATION "de_DE" RENAME TO german;

       To change the owner of the collation en_US to joe:

           ALTER COLLATION "en_US" OWNER TO joe;

COMPATIBILITY

       There is no ALTER COLLATION statement in the SQL standard.

SEE ALSO

       CREATE COLLATION (CREATE_COLLATION(7)), DROP COLLATION (DROP_COLLATION(7))

PostgreSQL 16.10                                      2025                                    ALTER COLLATION(7)