Re: NOT EXISTS or LEFT JOIN which one is better?

[Rich <rhdyes@xxxxxxxxx>]

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 <rummandba@xxxxxxxxx> 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?