ALTER COLLATION

ALTER COLLATION

7

SQL - Language Statements

ALTER COLLATION

change the definition of a collation

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 also be a direct or indirect member of 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](#sql-altercollation-notes) below.

Notes {#sql-altercollation-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
========
