简体中文

CREATE COLLATION

Defines a new collation.

Synopsis

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

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, 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. Database 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 ALTER COLLATION 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

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 Support in the PostgreSQL documentation for more information about collation support in Database.

When using the libc collation provider, the, locale must be applicable to the current database encoding. See CREATE DATABASE for the precise rules.

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

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 Database extension.