> Greetings.
>
> I was wondering if somone out there could shed some light on a query
> performance issie I have. I have a large lookup table that I query
> with nested selects to gain the INTERSECT result from.
>
> the bigger this table gets the slower the performance.
>
> 1. is creating a temp table and only intersecting from this a good idea?
>
> 2. does having a where clause in your select before your nested
> intersects change the amount of work the query
>
> i.e. select person_id from person where person_id < 5000 And
> person_id IN as opposed to select person_id from person where
> person_id IN(etc)
>
> thoughts?
person_id<5000 probably won't help - postgres will use index on exact
person_id if possible.
Anyway - for large queries try change IN (...) into EXISTS (...), or just
into explicit join if possible. IN clause is rather slow for bigger amount of
data.
Regards,
Tomasz Myrta
