CREATE COLLATION

CREATE COLLATION

7

SQL - Language Statements

CREATE COLLATION

define a new collation

CREATE COLLATION \[ IF NOT EXISTS \]

name

( \[ LOCALE =

locale

, \] \[ LC\_COLLATE =

lc\_collate

, \] \[ LC\_CTYPE =

lc\_ctype

, \] \[ PROVIDER =

provider

, \] \[ DETERMINISTIC =

boolean

, \] \[ VERSION =

version

\] ) CREATE COLLATION \[ IF NOT EXISTS \]

name

FROM

existing\_collation

Description {#sql-createcollation-description}
===========

`CREATE COLLATION` defines a new collation using the specified operating
system locale settings, or by copying an existing collation.

To be able to create a collation, you must have `CREATE` privilege on
the destination schema.

Parameters
==========

`IF NOT EXISTS`

:   Do not throw an error if a collation with the same name already
    exists. A notice is issued in this case. Note that there is no
    guarantee that the existing collation is anything like the one that
    would have been created.

name

:   The name of the collation. The collation name can be
    schema-qualified. If it is not, the collation is defined in the
    current schema. The collation name must be unique within that
    schema. (The system catalogs can contain collations with the same
    name for other encodings, but these are ignored if the database
    encoding does not match.)

locale

:   This is a shortcut for setting `LC_COLLATE` and `LC_CTYPE` at once.
    If you specify this, you cannot specify either of those parameters.

lc\_collate

:   Use the specified operating system locale for the `LC_COLLATE`
    locale category.

lc\_ctype

:   Use the specified operating system locale for the `LC_CTYPE` locale
    category.

provider

:   Specifies the provider to use for locale services associated with
    this collation. Possible values are: `icu`,ICU `libc`. `libc` is the
    default. The available choices depend on the operating system and
    build options.

`DETERMINISTIC`

:   Specifies whether the collation should use deterministic
    comparisons. The default is true. A deterministic comparison
    considers strings that are not byte-wise equal to be unequal even if
    they are considered logically equal by the comparison. PostgreSQL
    breaks ties using a byte-wise comparison. Comparison that is not
    deterministic can make the collation be, say, case- or
    accent-insensitive. For that, you need to choose an appropriate
    `LC_COLLATE` setting *and* set the collation to not deterministic
    here.

    Nondeterministic collations are only supported with the ICU
    provider.

version

:   Specifies the version string to store with the collation. Normally,
    this should be omitted, which will cause the version to be computed
    from the actual version of the collation as provided by the
    operating system. This option is intended to be used by `pg_upgrade`
    for copying the version from an existing installation.

    See also [???](#sql-altercollation) for how to handle collation
    version mismatches.

existing\_collation

:   The name of an existing collation to copy. The new collation will
    have the same properties as the existing one, but it will be an
    independent object.

Notes {#sql-createcollation-notes}
=====

`CREATE COLLATION` takes a `SHARE ROW
   EXCLUSIVE` lock, which is self-conflicting, on the pg\_collation
system catalog, so only one `CREATE COLLATION` command can run at a
time.

Use `DROP COLLATION` to remove user-defined collations.

See [???](#collation-create) for more information on how to create
collations.

When using the `libc` collation provider, the locale must be applicable
to the current database encoding. See [???](#sql-createdatabase) for the
precise rules.

Examples {#sql-createcollation-examples}
========

To create a collation from the operating system locale `fr_FR.utf8`
(assuming the current database encoding is `UTF8`):

    CREATE COLLATION french (locale = 'fr_FR.utf8');

To create a collation using the ICU provider using German phone book
sort order:

    CREATE COLLATION german_phonebook (provider = icu, locale = 'de-u-co-phonebk');

To create a collation from an existing collation:

    CREATE COLLATION german FROM "de_DE";

This can be convenient to be able to use operating-system-independent
collation names in applications.

Compatibility {#sql-createcollation-compat}
=============

There is a `CREATE COLLATION` statement in the SQL standard, but it is
limited to copying an existing collation. The syntax to create a new
collation is a PostgreSQL extension.

See Also {#sql-createcollation-seealso}
========
