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).
In SQL Database, login data required to authenticate a connection and server-level firewall rules are temporarily cached in each database. This cache is periodically refreshed. To force a refresh of the authentication cache and make sure that a database has the latest version of the logins table, execute DBCC FLUSHAUTHCACHE (Transact-SQL).
Requires ALTER ANY LOGIN permission on the server.
A. Dropping a login
The following example drops the login
DROP LOGIN WilliJo; GO