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

Source table can be anything, such as:

MERGE 
   member_topic AS target
USING 
   (SELECT @Variable1, @Variable2, @Variable3) AS source(Col1, Col2, Col3)
ON 
   target.mt_member = source.Col1 
   AND source.Col1 = 0 
   AND source.Col2 = 110
WHEN MATCHED THEN 
   UPDATE SET mt_notes = 'test'
WHEN NOT MATCHED THEN 
   INSERT (mt_member, mt_topic, mt_notes) VALUES (0, 110, 'test');

Obviously, in the nested source select you can do many more things. Select from a view, a function, a table variable, a CTE even.

As for the bonus question, you answered your own question.

Sometimes,for very large tables, I also use the ROWLOCK hint on the target table, to at least try not to lock the entire table in case of updates:

MERGE 
   member_topic WITH (ROWLOCK) AS target

Related to the bonus question not working, here's a working sample. I renamed some of the objects, of course.

DECLARE @Variable1 AS INT;
SET @Variable1 = 1234;

MERGE dbo.Table1 WITH(ROWLOCK) target
USING(SELECT @Variable1) source(Key)
ON target.[Key] = source.[Key]
WHEN MATCHED THEN
    UPDATE SET
    Col1 = @SomeVar1,
    Col2 = @SomeVar2
WHEN NOT MATCHED THEN
INSERT 
        ([Key]
        ,[Col1]
        ,[Col2])
    VALUES
        (@Variable1
        ,@SomeVar1
        ,@SomeVar2);