ALTER USER (Transact-SQL)
Renames a database user or changes its default schema.
If DEFAULT_SCHEMA is left undefined, the user will have dbo as its default schema. DEFAULT_SCHEMA can be set to a schema that does not currently occur in the database. Therefore, you can assign a DEFAULT_SCHEMA to a user before that schema is created. DEFAULT_SCHEMA cannot be specified for a user who is mapped to a Windows group, a certificate, or an asymmetric key.
The value of DEFAULT_SCHEMA is ignored if the user is a member of the sysadmin fixed server role. All members of the sysadmin fixed server role have a default schema of dbo.
You can change the name of a user who is mapped to a Windows login or group only when the SID of the new user name matches the SID that is recorded in the database. This check helps prevent spoofing of Windows logins in the database.
The WITH LOGIN clause enables the remapping of a user to a different login. Users without a login, users mapped to a certificate, or users mapped to an asymmetric key cannot be re-mapped with this clause. Only SQL users and Windows users (or groups) can be remapped. The WITH LOGIN clause cannot be used to change the type of user, such as changing a Windows account to a SQL Server login.
The name of the user will be automatically renamed to the login name if the following conditions are true.
The user is a Windows user.
The name is a Windows name (contains a backslash).
No new name was specified.
The current name differs from the login name.
Otherwise, the user will not be renamed unless the caller additionally invokes the NAME clause.
A user who has ALTER ANY USER permission can change the default schema of any user. A user who has an altered schema might unknowingly select data from the wrong table or execute code from the wrong schema.
The name of a user mapped to a SQL Server login, a certificate, or an asymmetric key cannot contain the backslash character (\).
Beginning with SQL Server 2005, the behavior of schemas changed. As a result, code that assumes that schemas are equivalent to database users may no longer return correct results. Old catalog views, including sysobjects, should not be used in a database in which any of the following DDL statements have ever been used: CREATE SCHEMA, ALTER SCHEMA, DROP SCHEMA, CREATE USER, ALTER USER, DROP USER, CREATE ROLE, ALTER ROLE, DROP ROLE, CREATE APPROLE, ALTER APPROLE, DROP APPROLE, ALTER AUTHORIZATION. In such databases you must instead use the new catalog views. The new catalog views take into account the separation of principals and schemas that was introduced in SQL Server 2005. For more information about catalog views, see Catalog Views (Transact-SQL).
A. Changing the name of a database user
The following example changes the name of the database user Mary5 to Mary51.
USE AdventureWorks; ALTER USER Mary5 WITH NAME = Mary51; GO
B. Changing the default schema of a user
The following example changes the default schema of the user Mary51 to Purchasing.
USE AdventureWorks; ALTER USER Mary51 WITH DEFAULT_SCHEMA = Purchasing; GO