From: | Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Hannu Krosing <hannu(at)skype(dot)net>, Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Order by optimisations? |
Date: | 2005-07-15 05:42:38 |
Message-ID: | 42D74CCE.3030609@familyhealth.com.au |
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Lists: | pgsql-hackers |
> Well, date evidently isn't the high-order key of this index. But why
> exactly are you worried about a sort of 2 rows?
Aha that's nailed it:
usa=> explain select * from users_myfoods_map where user_id=1 and date
between '2003-11-03' and '2003-11-03' order by user_id, date;
QUERY PLAN
-------------------------------------------------------------------------------------------------------------
Index Scan using users_myfoods_map_user_id_date_key on
users_myfoods_map (cost=0.00..3.78 rows=1 width=22)
Index Cond: ((user_id = 1) AND (date >= '2003-11-03'::date) AND
(date <= '2003-11-03'::date))
(2 rows)
I don't care about this particular result. But imagine it running
thousands of times a minute, with result sets between 0 and 50 rows...
Chris
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