title: MERGE - conditional "WHEN MATCHED" OUTPUT
body: <p>The following code shows two <code>WHEN MATCHED</code>-clauses.
  The first one matches when only the <code>DATETIME</code>-column 'updatedAt' is changed.
  This should update the target, however I don't want this marked in the <code>OUTPUT</code>. The second one matches when there are other changes in the given match, this should lead to an <code>OUTPUT</code>.</p>
  
  <pre><code>MERGE [Target].dbo.[clients] AS target
  USING [Source].dbo.[clients] AS source
  ON target.[objectId]=source.[objectId]
  WHEN MATCHED AND NOT EXISTS (
                      SELECT source.firstName, ...
                      EXCEPT
                      SELECT target.firstName, ...
                  ) AND source.updatedAt &lt;&gt; target.updatedAt
  THEN 
      UPDATE SET --THIS UPDATE SHOULD NOT LEAD TO AN OUTPUT WITH $ACTION = 'UPDATE'
          target.updatedAt = source.updatedAt
  WHEN MATCHED AND EXISTS (
                      SELECT source.firstName, ... , source.updatedAt
                      EXCEPT
                      SELECT target.firstName, ... , target.updatedAt
                  )
  THEN
      UPDATE SET --THIS UPDATE SHOULD LEAD TO AN OUTPUT WITH $ACTION = 'UPDATE'
          target.[firstName]=source.[firstName], ...
  WHEN NOT MATCHED BY TARGET
  THEN
      INSERT ([objectId],[firstName], ... ,[updatedAt]) VALUES ([objectId],[firstName], ... ,[updatedAt])
  WHEN NOT MATCHED BY SOURCE
  THEN
      DELETE
  
  OUTPUT 
      $ACTION ChangeType
      , ISNULL(
          inserted.objectId
          , deleted.objectId
      ) AS objectId
      , GETDATE() AS DateTimeChanged
  ;
  </code></pre>
  
  <p>This is achievable by outputting all source and target columns and putting the <code>MERGE</code> in a subquery, to make the comparison in a main query, e.g.:</p>
  
  <pre><code>WHERE NOT (
      [ChangeType]='UPDATE' 
      AND [src objectId]=[tgt objectId] 
      AND [src firstName]=[tgt firstName] 
      AND ... 
      AND [src updatedAt]&lt;&gt;[tgt updatedAt]
  )
  </code></pre>
  
  <p>However, I feel there should be a better way, since I am able to declare two different <code>WHEN MATCHED</code>-clauses. Is there any better way?</p>