Tuning this query

Question

Hi,
Can anybody please help me in tuning this query?
update tablec c set c.col1 = (select b.col1 from tableb b where c.col2 = b.col2 ) where
c.col2 in (select distinct a.col1 from tablec a, tableb b where a.col2 = b.col2 and a.col1 != b.col1 )
When i use "alter session force parallel DML" before running this query it takes only seconds, but when i use parallel hint or run it without hint, its running for hours.
Thanks for your Help

Answer 1

Hi itssan,
You could try EXISTS.
I think this is the same:
update tablec c
   set c.col1 =
          (select b.col1
             from tableb b
            where b.col2 = c.col2)
where exists (select null
                 from tablec a, tableb b
                where a.col2 = b.col2
                  and a.col1 != b.col1
                  and a.col1 = c.col2);Regards
Peter