man page ALTER_COLLATION section 7

ALTER COLLATION(7)       PostgreSQL 16.7 Documentation      ALTER COLLATION(7)

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.