title: case when exists in oracle update query
body: <p>I have update query like</p>
  
  <pre><code>update dedupctntest a set a.city = case when exists(
  select b.shortname from DEDUPADDRESSDICT where lower(a.city) =lower(b.shortname) and rownum = 1) b  then
  b.fullname else a.city end;
  </code></pre>
  
  <p>but it will give <code>missing keyword</code> error </p>
  
  <p>can anybody tell what is wrong in that ?</p>