From: elziko@NOTSPAMMINGyahoo.co.uk   
      
   I have two tables TAB_A and TAB_B. I want to update COL_1 in TAB_A to a   
   certain value but only for rows where the value COL_2 in TAB_A is also found   
   in COL_2 of TAB_B.   
      
   This is what I have but it seems to then set COL_1 of TAB_A to a NULL if its   
   not found in TAB_B. In this case I just want to leave that row unchanged.   
      
   UPDATE tab_a   
   SET col_1 = 'NEWVALUE'   
   WHERE EXISTS (SELECT 1   
                                   FROM tab_a a, tab_b b   
                                   WHERE a.col_2 = b.col_2)   
                                   AND col_1 IS NULL;   
      
   Any ideas to what I'm doing wrong?   
      
   --   
      
   Cheers,   
      
   elziko   
      
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