title: update with exists in oracle
body: <p>I have this query :</p>
  <pre><code>update rexcms e
     set e.cocnd=(select r.cocnd
                    from rexcms r
                   where NVL(r.marche,'*')=NVL(e.marche,'*')
                     and r.cocrd= e.cocrd
                     and r.cocol=e.cocol
                     and r.cocol='CHBIL'
                     and r.marche='CBOT')
   where e.cocol ='CDVHB' ;
  </code></pre>
  <p>how can use EXISTS to optimize it</p>