Re: small table, huge table, and a join = slow and tough query. cake inside!

On May 28, 2008, at 9:27 PM, edfialk wrote:

> example rows from huge table (almost 900,000 rows):
> fips, pollutant, value

That's not really huge in comparison with other pgsql databases.
There are terabyte installations out there ;)

> SELECT small.fips, small.geom, small.name, SUM(huge.value) from small
> JOIN huge on huge.fips = small.fips WHERE (SUM(huge.value)) > 500 AND
> huge.pollutant='co';
>
> wonder if that makes sense.  Obviously, can't have an aggregate in
> where clause, so I've tried a couple WHERE (SELECT) kind of things,
> nothing working out too well.
>
> So first, if anyone has any idea on the best way I can do a WHERE
> (sum(huge.value) > 500)
> or...
> any ideas on how I could speed up the query, I would be so extremely
> grateful.

That's what GROUP BY and HAVING are for:

SELECT fips, small.geom, small.name, SUM(huge.value)
FROM small
JOIN huge USING (fips)
WHERE huge.pollutant='co'
GROUP BY fips, small.geom, small.name
HAVING SUM(huge.value) > 500;

Guessing from your performance problem you may not have an index on
huge.fips? And did you vacuum/analyse those tables anytime recently?

Alban Hertroys

--
If you can't see the forest for the trees,
cut the trees and you'll see there is no forest.


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