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Set or change the database collation

  • Článek

Applies to: SQL Server Azure SQL Managed Instance

This article describes how to set or change the database collation by using SQL Server Management Studio (SSMS) or Transact-SQL.

If no database collation is specified, the server collation is used.

Recommendations

You can find the supported collation names in Windows Collation Name and SQL Server Collation Name; or you can use the sys.fn_helpcollations system function.

When you change the database collation, you change:

  • Any char, varchar, text, nchar, nvarchar, or ntext columns in system tables are changed to the new collation.

  • All existing char, varchar, text, nchar, nvarchar, or ntext parameters and scalar return values for stored procedures and user-defined functions are changed to the new collation.

  • The char, varchar, text, nchar, nvarchar, or ntext system data types, and all user-defined data types based on these system data types, are changed to the new default collation.

You can change the collation of any new objects that are created in a user database by using the COLLATE clause of the ALTER DATABASE statement. This statement does not change the collation of the columns in any existing user-defined tables. These can be changed by using the COLLATE clause of ALTER TABLE.

Permissions

To create a new database, you need the CREATE DATABASE permission in the master database, or the CREATE ANY DATABASE, or ALTER ANY DATABASE permission.

To change the collation of an existing database, you need the ALTER permission on the database.

Set or change the database collation

You can set or change the database collation using SQL Server Management Studio (SSMS), or Transact-SQL (T-SQL).

You can specify the collation for a new database or update the collation for an existing database by using SQL Server Management Studio (SSMS).

In SQL Server Management Studio, open Object Explorer, connect to an instance of the SQL Server Database Engine, expand that instance, and then expand Databases:

  • For a new database: Right-click Databases and then select New Database. If you don't want the default collation, select the Options page, and select a collation from the Collation dropdown list.
  • For an existing database: Right-click the database that you want and select Properties. Select the Options page, and select a collation from the Collation dropdown list.

Data after changing the collation

Important

Changing the collation of a database or individual columns does not modify the underlying data already stored in existing tables. Unless your application explicitly handles data conversion and comparison between different collations, it is recommended that you transition existing data in the database to the new collation. This removes the risk that applications might incorrectly modify data, resulting in possible wrong results or silent data loss.

When a database collation is changed, only new tables inherit the new database collation by default. There are several alternatives to convert existing data to the new collation:

  • Convert data in-place. To convert the collation for a column in an existing table, see Set or Change the Column Collation. This operation is easy to implement, but might become a blocking issue for large tables and busy applications. See the following example for an in-place conversion of the MyString column to a new collation:

    ALTER TABLE dbo.MyTable
    ALTER COLUMN MyString VARCHAR(50) COLLATE Latin1_General_100_CI_AI_SC_UTF8;

  • Copy data to new tables that use the new collation, and replace original tables in the same database. Create a new table in the current database that will inherit the database collation, copy the data between the old table and the new table, drop the original table, and rename the new table to the name of the original table. This is a faster operation than an in-place conversion, but might become a challenge when handling complex schemas with dependencies such as Foreign Key constraints, Primary Key constraints, and Triggers. It would also require a final data synchronization between the original and the new table before the final cut-off, if data continues to be changed by applications. See the following example for a "copy and replace" conversion of the MyString column to a new collation:

    CREATE TABLE dbo.MyTable2 (MyString VARCHAR(50) COLLATE Latin1_General_100_CI_AI_SC_UTF8);

INSERT INTO dbo.MyTable2
SELECT * FROM dbo.MyTable;

DROP TABLE dbo.MyTable;

EXEC sp_rename 'dbo.MyTable2', 'dbo.MyTable';

  • Copy data to a new database that uses the new collation, and replace the original database. Create a new database using the new collation, and transfer the data from the original database via tools like Integration Services or the Import/Export Wizard in SQL Server Management Studio. This is a simpler approach for complex schemas. It would also require a final data synchronization between the original and the new databases before the final cut-off, if data continues to be changed by applications.

Limitations

  • 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 can't be used with the COLLATE clause to change the collation of a database or server instance.

  • If the specified collation or the collation used by the referenced object uses a code page that isn't supported by Windows, the Database Engine displays an error.

  • Server-level collation in Azure SQL Managed Instance can be specified when the instance is created and can't be changed later. Learn more in Set or change the server collation.

Important

The ALTER DATABASE COLLATE statement is not supported on Azure SQL Database. Specify database collation and catalog collation at the time of CREATE DATABASE.

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