ALTER COLLATION — change the definition of a collation
ALTER COLLATIONname
REFRESH VERSION ALTER COLLATIONname
RENAME TOnew_name
ALTER COLLATIONname
OWNER TO {new_owner
| CURRENT_ROLE | CURRENT_USER | SESSION_USER } ALTER COLLATIONname
SET SCHEMAnew_schema
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.)
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.
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.
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;
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;
There is no ALTER COLLATION
statement in the SQL standard.
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