Re: NOT IN >2hrs vs EXCEPT < 2 sec.

On Wed, Jan 28, 2009 at 11:37 PM, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>wrote:

> On Thu, Jan 29, 2009 at 12:01 AM, Kevin Traster <kevin(at)mffais(dot)com> wrote:
> > 2 questions:
> >
> > 1) Different costs for same actions. Doing an explain on 2 nearly
> identical
> > queries both involving the same Index scan on same table has 2 widely
> > different costs for same Index scan 303375872.86 vs. 12576.70
>
> Pretty sure this is a FAQ by now.
>
> not in and except treat nulls differently. If you table has nullable
> fields and nulls would break your query, then not in () is a bad
> choice. Therefore, effort to optimize had been placed into except,
> which is distinctly, symantically different from not in ().
>
> It seems like some shift in the pg community has happened where we're
> suddenly getting a lot of folks who came from a database where not in
> and except are treated the same, even though they most definitely do
> not mean the same thing.
>