How To Find the Login Name Linked to a Given User Name in SQL Server?

If you know a user name in a database and you want to find out which login name is linked this user name, you need to check the Security ID (SID) of the user name based on the following rules:

• Each login name is associated a unique SID.
• When a user name is linked to a login name, the login name's SID is copied to the user name.

So the login name linked to a user name must have the SID as the user name. The tutorial exercise below shows you how to find the login name that is linked to the user name "Fyi_User":

-- Login with sa

USE FyiCenterData;
GO

SELECT u.name AS User_Name, l.name AS Login_Name, u.sid 
   FROM sys.server_principals l, 
      sys.database_principals u
   WHERE l.sid = u.sid
      AND u.name = 'Fyi_User';
GO
User_Name  Login_Name  sid
---------- ----------- ----------------------------------
Fyi_User   Fyi_Login   0x5EB8701EAEBAA74F86FCF5BD8E37B8C5
(1 row(s) affected)

⇒ Verifying a User Name with SQLCMD Tool in SQL Server

⇐ sys.database_principals - Listing All User Names in SQL Server

⇑ Managing Security, Login and User in SQL Server

⇑⇑ SQL Server Database Tutorials