alter_collation(7)

—

NAME

ALTER_COLLATION - change the definition of a collation

SYNOPSIS

bash

ALTER COLLATION \nname\n REFRESH VERSION
ALTER COLLATION \nname\n RENAME TO \nnew_name\n
ALTER COLLATION \nname\n OWNER TO { \nnew_owner\n | CURRENT_ROLE | CURRENT_USER | SESSION_USER }
ALTER COLLATION \nname\n SET SCHEMA \nnew_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

new_name

new_owner

new_schema

REFRESH VERSION

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:

bash

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.

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:

bash

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

EXAMPLES

To rename the collation de_DE to german:

bash

ALTER COLLATION "de_DE" RENAME TO german;

To change the owner of the collation en_US to joe:

bash

ALTER COLLATION "en_US" OWNER TO joe;

COMPATIBILITY

There is no ALTER COLLATION statement in the SQL standard.