Checking if a SQL Server login already exists

Here's a way to do this in SQL Server 2005 and later without using the deprecated syslogins view:

IF NOT EXISTS     (SELECT name       FROM master.sys.server_principals     WHERE name = 'LoginName')BEGIN    CREATE LOGIN [LoginName] WITH PASSWORD = N'password'END

The server_principals view is used instead of sql_logins because the latter doesn't list Windows logins.

If you need to check for the existence of a user in a particular database before creating them, then you can do this:

USE your_db_nameIF NOT EXISTS    (SELECT name     FROM sys.database_principals     WHERE name = 'Bob')BEGIN    CREATE USER [Bob] FOR LOGIN [Bob] END

From here

If not Exists (select loginname from master.dbo.syslogins     where name = @loginName and dbname = 'PUBS')Begin    Select @SqlStatement = 'CREATE LOGIN ' + QUOTENAME(@loginName) + '     FROM WINDOWS WITH DEFAULT_DATABASE=[PUBS], DEFAULT_LANGUAGE=[us_english]')    EXEC sp_executesql @SqlStatementEnd

As a minor addition to this thread, in general you want to avoid using the views that begin with sys.sys* as Microsoft is only including them for backwards compatibility. For your code, you should probably use sys.server_principals. This is assuming you are using SQL 2005 or greater.