title: MERGE table, do nothing when matched
body: <p>I have a table <code>DOMAINS</code> in 2 different schemas with columns <code>ID</code>, <code>NAME</code>,<code>CODE</code>,<code>DESCRIPTION</code>.</p>
  
  <p>For any <code>NAME</code> exist in new schema, it should use existing <code>ID</code> without any merge; for those new <code>NAME</code> records, it should insert with <code>ID</code> from old schema.</p>
  
  <pre><code>MERGE INTO DOMAINS A
  USING (SELECT ID,NAME,CODE,DESCRIPTION FROM &lt;Old Schema 6.1&gt;.DOMAINS@DB_MIG_61_TO_74) B
  ON(A.NAME = B.NAME)
  WHEN MATCHED **&lt;do nothing&gt;**
  WHEN NOT MATCHED THEN INSERT(A.ID,A.NAME,A.CODE,A.DESCRIPTION) 
  VALUES(B.ID,B.NAME,B.CODE,B.DESCRIPTION);
  </code></pre>
  
  <p><em>How can i intepret the portion of <code>do nothing</code> in above query?</em> </p>