DROP LOGIN (Transact-SQL)
Removes a SQL Server login account.
DROP LOGIN login_name
Specifies the name of the login to be dropped.
A login cannot be dropped while it is logged in. A login that owns any securable, server-level object, or SQL Server Agent job cannot be dropped.
You can drop a login to which database users are mapped; however, this will create orphaned users. For more information, see Troubleshoot Orphaned Users (SQL Server).
Requires ALTER ANY LOGIN permission on the server.
The following example drops the login WilliJo.
DROP LOGIN WilliJo; GO