DROP LOGIN (Transact-SQL)
Removes a SQL Server login account.
Applies to: SQL Server (SQL Server 2008 through current version), Azure SQL Database.
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).