title: Append query should only append if value not present
body: <p>I'm trying to run an append query, but it should only run if there isn't already a value present in order to avoid duplicates. </p>
  
  <p>I heard you can do this with a Where clause, but not sure how to implement it, as what I've tried so far (see code below) isn't really giving me the right result. </p>
  
  <p>It needs to check if there already exists a value in Saneringsmetodekode, if there is one, it should do nothing. </p>
  
  <pre><code>INSERT INTO NySaneringsData ( DelledningsID, SaneringsmetodeKode )
  SELECT SaneringsprojektImport.DelledningsID, SaneringsprojektImport.SaneringsmetodeKode
  FROM NySaneringsData RIGHT JOIN SaneringsprojektImport ON NySaneringsData.DelledningsID = SaneringsprojektImport.DelledningsID
  WHERE (((SaneringsprojektImport.SaneringsmetodeKode) Is Not Null) AND ((Exists (SELECT * FROM NySaneringsData WHERE NySaneringsData.SaneringsmetodeKode = SaneringsprojektImport.SaneringsmetodeKode))=False))
  ORDER BY SaneringsprojektImport.DelledningsID;
  </code></pre>
  
  <p>Any help would be much appreciated. </p>