The identity of the login remains authenticated as long as the connection is maintained. If the user doesn't have a default schema, but the user is a member of a group that has a default schema, the default schema of the group will be used. The WITH LOGIN clause can't 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.Otherwise, the user won't be renamed unless the caller additionally invokes the NAME clause.The name of a user mapped to a SQL Server login, a certificate, or an asymmetric key can't contain the backslash character (\).Beginning with SQL Server 2005, the behavior of schemas changed. An ALTER LOGIN statement that has this combination of options will fail.You cannot use ALTER_LOGIN with the DISABLE argument to deny access to a Windows group. Regarding "Windows identifiers or ... why you want to create a SQL auth user that is mapped to one": by chopping off the last 12 bytes, there is no mapping between them.A SQL Server login's SID is merely an arbitrary 16-bytes.

If login is not specified, information about the current security context is returned. Open a new query in SQL Server Management Studio and execute the following command: use go ALTER USER sde WITH login = sde go.

Otherwise, the statement will fail.If CHECK_POLICY is set to OFF, CHECK_EXPIRATION cannot be set to ON. The WITH LOGIN option can only be used if Azure AD logins are present.The name of the user will be automatically renamed to the login name if the following conditions are true.Otherwise, the user won't be renamed unless the caller additionally invokes the NAME clause.The name of a user mapped to a SQL Server login, a certificate, or an asymmetric key can't contain the backslash character (\).Beginning with SQL Server 2005, the behavior of schemas changed.

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. A user with the KILL DATABASE CONNECTION permission can explicitly terminate a connection to SQL Database by using the KILL command. This option may only be specified in a contained database and only for contained users.Suppresses cryptographic metadata checks on the server in bulk copy operations.

Users without a login, users mapped to a certificate, or users mapped to an asymmetric key can't be remapped with this clause.
Changes the properties of a SQL Server login account.In the following row, select the product name you're interested in, and only that product’s information is displayed.ENABLE | DISABLE For a Windows Authentication login, this includes information about membership in Windows groups. For more information, see The current user password that will be replaced by 'Specifies a default language to be assigned to the user. The new catalog views take into account the separation of principals and schemas that was introduced in SQL Server 2005. This option should only be used for login synchronization between two servers. If no default schema can be determined for a user, the DEFAULT_SCHEMA can be set to a schema that doesn't currently occur in the database. In such databases you must instead use the new catalog views.

As a result, code that assumes that schemas are equivalent to database users may no longer return correct results. Applies to SQL Server logins only. If no default schema can be determined for a user, the DEFAULT_SCHEMA can be set to a schema that doesn't currently occur in the database.