Al I have looked at this before and I am not sure the effort is worth all the thought about it. Let your explain tell you which is better. I read this link a year ago. http://stackoverflow.com/questions/227037/can-i-get-better-performance-using-a-join-or-using-exists
On Sun, Apr 29, 2012 at 5:27 AM, AI Rumman <rumman...@gmail.com> wrote: > I can write a query to solve my requirement in any of the followings :- > > 1. > select * > from a > where NOT EXISTS > ( > select 1 > from b > where a.id = b.id) > union all > select * > from b > > > 2. > select > ( > case when b.id is not null then > b.id > else > a.id > ) as id > from a > left join b > on a.id = b.id > > Any one please tell me which one is better? >
