Re: Forcing filter/join order?

Stephan,

> Can you give more information? I know that I'm not exactly certain what
> the situation is from the above and the original query/explain piece.
>

Believe me, if I posted the query it wouldn't help. Heck, I'd have trouble
following it without my notes.

a simplifed version:

SELECT events.*, cases.case_name
FROM events LEFT OUTER JOIN cases ON events.case_id = cases.case_id
WHERE (event_date >= '2004-03-05' OR (event_date + duration) <= '2004-02-18')
AND events.status <> 0;

... this is to get me all vaild events which overlap with the range
'2004-02-18' to '2004-03-05'.

I had thought, in 7.4, that adding an index on (event_date, (event_date +
duration)) would improve the execution of this query. It doesn't,
presumably because the multi-column index can't be used for both ascending
and descending sorts at the same time, and event_date >= '2004-03-05' isn't
selective enough.

There was a workaround for this posted on hackers about a year ago as I
recally, that involved creating custom operators for indexing. Too much
trouble when there's a hackish workaround (due to the fact that events have
to be less than a month long).

--
-Josh Berkus
Aglio Database Solutions
San Francisco