Re: Why the "where NOT EXISTS" does not work?

Our distinguished colleague, "C Chang" scribed:

>Which Proccess is more efficient?

>select a from A_Table
>minus
>select a from B_table

>or

>select a from test1
>where not exists
>(select 1 from test2
> where test1.a = test2.b)

The second construction is a correlated subquery, which I've been told is inefficient, owing to exhaustive comparisons. Does the 'minus' set operator do any optimization? - not sure.

-- 
Roy                 
kl7_at_rahul.net (USA)