COLLATE (Transact-SQL)

Artykuł
02/13/2015

Is a clause that can be applied to a database definition or a column definition to define the collation, or to a character string expression to apply a collation cast.

Ikona łącza do tematu Transact-SQL Syntax Conventions

Składnia

COLLATE { <collation_name> | database_default }
<collation_name> :: = 
     { Windows_collation_name } | { SQL_collation_name }

Arguments

collation_name
Is the name of the collation to be applied to the expression, column definition, or database definition. collation_name can be only a specified Windows_collation_name or a SQL_collation_name. collation_name must be a literal value. collation_name cannot be represented by a variable or expression.

Windows_collation_name is the collation name for a Windows Collation Name.

SQL_collation_name is the collation name for a SQL Server Collation Name.

When applying a collation at the database definition level, Unicode-only Windows collations cannot be used with the COLLATE clause.
database_default
Causes the COLLATE clause to inherit the collation of the current database.

Uwagi

The COLLATE clause can be specified at several levels. These include the following:

Creating or altering a database.

You can use the COLLATE clause of the CREATE DATABASE or ALTER DATABASE statement to specify the default collation of the database. You can also specify a collation when you create a database using SQL Server Management Studio. If you do not specify a collation, the database is assigned the default collation of the instance of SQL Server.

[!UWAGA]

Windows Unicode-only collations can only be used with the COLLATE clause to apply collations to the nchar, nvarchar, and ntext data types on column-level and expression-level data; they cannot be used with the COLLATE clause to change the collation of a database or server instance.
Creating or altering a table column.

You can specify collations for each character string column using the COLLATE clause of the CREATE TABLE or ALTER TABLE statement. You can also specify a collation when you create a table using SQL Server Management Studio. If you do not specify a collation, the column is assigned the default collation of the database.

You can also use the database_default option in the COLLATE clause to specify that a column in a temporary table use the collation default of the current user database for the connection instead of tempdb.
Casting the collation of an expression.

You can use the COLLATE clause to apply a character expression to a certain collation. Character literals and variables are assigned the default collation of the current database. Column references are assigned the definition collation of the column.

The collation of an identifier depends on the level at which it is defined. Identifiers of instance-level objects, such as logins and database names, are assigned the default collation of the instance. Identifiers of objects within a database, such as tables, views, and column names, are assigned the default collation of the database. For example, two tables with names different only in case may be created in a database with case-sensitive collation, but may not be created in a database with case-insensitive collation. For more information, see Database Identifiers.

Variables, GOTO labels, temporary stored procedures, and temporary tables can be created when the connection context is associated with one database, and then referenced when the context has been switched to another database. The identifiers for variables, GOTO labels, temporary stored procedures, and temporary tables are in the default collation of the server instance.

The COLLATE clause can be applied only for the char, varchar, text, nchar, nvarchar, and ntext data types.

COLLATE uses collate_name to refer to the name of either the SQL Server collation or the Windows collation to be applied to the expression, column definition, or database definition. collation_name can be only a specified Windows_collation_name or a SQL_collation_name and the parameter must contain a literal value. collation_name cannot be represented by a variable or expression.

Collations are generally identified by a collation name, except in Setup. In Setup you instead specify the root collation designator (the collation locale) for Windows collations, and then specify sort options that are sensitive or insensitive to case or accents.

You can execute the system function fn_helpcollations to retrieve a list of all the valid collation names for Windows collations and SQL Server collations:

SELECT name, description
FROM fn_helpcollations();

SQL Server can support only code pages that are supported by the underlying operating system. When you perform an action that depends on collations, the SQL Server collation used by the referenced object must use a code page supported by the operating system running on the computer. These actions can include the following:

Specifying a default collation for a database when you create or alter the database.
Specifying a collation for a column when you create or alter a table.
When restoring or attaching a database, the default collation of the database and the collation of any char, varchar, and text columns or parameters in the database must be supported by the operating system.

Code page translations are supported for char and varchar data types, but not for text data type. Data loss during code page translations is not reported.

If the collation specified or the collation used by the referenced object uses a code page not supported by Windows, SQL Server displays an error.

Examples

A. Specifying collation during a select

The following example creates a simple table and inserts 4 rows. Then the example applies two collations when selecting data from the table, demonstrating how Chiapas is sorted differently.

CREATE TABLE Locations
(Place varchar(15) NOT NULL);
GO
INSERT Locations(Place) VALUES ('Chiapas'),('Colima')
                             , ('Cinco Rios'), ('California');
GO
--Apply an typical collation
SELECT Place FROM Locations
ORDER BY Place
COLLATE Latin1_General_CS_AS_KS_WS ASC;
GO
-- Apply a Spanish collation
SELECT Place FROM Locations
ORDER BY Place
COLLATE Traditional_Spanish_ci_ai ASC;
GO

Here are the results from the first query.

Place

-------------

California

Chiapas

Cinco Rios

Colima

Here are the results from the second query.