title: how to update a row with another row if column values are null in SQL
body: <p>i have 4 column, 
  Sup1,Sup2,Sup3 and Vers.</p>
  
  <p>i have to update Vers values from sup1, if sup1 null get values from sup2, if sup 2 null get values from sup3. if Sup1,Sup2,Sup3 are null then NULL.</p>
  
  <p>look like this :</p>
  
  <pre><code>sup1 sup2 sup3 vers
  1               1
        2         2
             3    3
  4     4    5    5
  0     0    0   NULL
  </code></pre>
  
  <p>i have tried this </p>
  
  <pre><code> update CRATEST set  
   --more next ( 4 to n ) columns here if required       
   Vers = (case when (Sup1 is null) then Sup2  
           when (Sup2 is null) then sup3 
           when (sup3 is null) then Sup1 else 'NULL' end);
  </code></pre>