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June 7, 2015

6/07/2015 03:47:00 AM
Oracle Tuning Tips
Watch Non-Indexed WHERE Conditions
Oracle evaluates Non-Indexed conditions linked by AND bottom up
Bad: select * from address where
                         areacode = 500003 and
                         type_nr = (select seq_nr from code_table where type = ‘HOME’)
Good: select * from address where
                         type_nr = (select seq_nr from code_table where type = ‘HOME’) and
                         areacode = 500003
Oracle evaluates Non-Indexed conditions linked by OR top down
Bad: select * from address where
                         type_nr = (select seq_nr from code_table where type = ‘HOME’) or
                         areacode = 500003
Good: select * from address where
                         areacode = 500003 or
                         type_nr = (select seq_nr from code_table where type = ‘HOME’)
Oracle Tuning Tips UNION/OR
Consider IN or UNION in place of OR  

i
 columns are not indexed, stick with OR
if columns are indexed, use IN or UNION in place of OR
IN example
Bad: select * from address where
                         state = 'AP‘ or
                         state = 'KL‘ or
                         state = 'KL‘
Good: select * from address where
                         state in ('AP','KL','KL')
UNION example
Bad: select * from address where
                         state = ‘KL’ or
                         areacode = 500003
Good: select * from address where
                         state = ‘KL’
               union
               select * from address where
                         areacode = 500003