What is USING in SQL Server 2008 MERGE syntax?

Question

Jacob asked the perfect question: give me the MERGE syntax.

Every answer out there immediately jumps to the most complicated case they can think of; obscuring the sy

Answer 1

Following on from Martin Smith's answer, you can upsert several explicit value rows at once simply by repeating the brackets, separating with a comma, eg,

MERGE Users WITH (HOLDLOCK)
USING (VALUES ('{77410DC5-7A3E-4F1A-82C6-8EFB3068DE66}',
      'iboyd',
      'Ian',
      'Boyd',
      'Windows'),
      ('{00000DC5-7A3E-4F1A-82C6-8EF452D2DE66}',
      'jsmith',
      'John',
      'Smith',
      'ActiveDirectory')) AS foo(UserGUID, Username, FirstName, LastName, AuthenticationMethod)
ON Users.UserName = foo.UserName
WHEN MATCHED THEN
  UPDATE SET Firstname = foo.FirstName,
             Lastname = foo.LastName
WHEN NOT MATCHED THEN
  INSERT (UserGUID,
          Username,
          FirstName,
          LastName,
          AuthenticationMethod)
  VALUES (UserGUID,
          Username,
          FirstName,
          LastName,
          AuthenticationMethod); 

Tested this on SQL Server 2012. (Would have added this as a comment but too many characters.)

I added a HOLDLOCK having seen this, because if you're using MERGE for UPSERT surely the point is locking, the syntax is certainly no clearer. See also Marcel's comment on ROWLOCK for large tables.

There was another post I found clearer than average, too.