Returns the login name associated with a security identification number (SID).
SUSER_SNAME ( [ server_user_sid ] )
Arguments ------- server_user_sid
Is the login security identification number. server_user_sid, which is optional, is varbinary(85). server_user_sid can be the security identification number of any SQL Server login or Microsoft Windows user or group. If server_user_sid is not specified, information about the current user is returned. If contains the word NULL, will return NULL.