Re: Slow query with backwards index scan
От | Tilmann Singer |
---|---|
Тема | Re: Slow query with backwards index scan |
Дата | |
Msg-id | 20070728192713.GH19392@tils.net обсуждение исходный текст |
Ответ на | Re: Slow query with backwards index scan (andrew@pillette.com) |
Ответы |
Re: Slow query with backwards index scan
Re: Slow query with backwards index scan |
Список | pgsql-performance |
* andrew@pillette.com <andrew@pillette.com> [20070728 21:05]: > Let's try putting the sort/limit in each piece of the UNION to speed them up separately. > > SELECT * FROM ( > (SELECT * FROM large_table lt > WHERE lt.user_id = 12345 > ORDER BY created_at DESC LIMIT 10) AS q1 > UNION > (SELECT * FROM large_table lt > WHERE user_id IN (SELECT contact_id FROM relationships WHERE user_id=12345) > ORDER BY created_at DESC LIMIT 10) AS q2 > ORDER BY created_at DESC LIMIT 10; It's not possible to use ORDER BY or LIMIT within unioned queries. http://www.postgresql.org/docs/8.2/static/sql-select.html#SQL-UNION Would that make sense at all given the way the postgresql planner works? Does that work in other DB's? Til
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