Group by, count, order by and limit
| От | Anuradha Ratnaweera |
|---|---|
| Тема | Group by, count, order by and limit |
| Дата | |
| Msg-id | 20030218042646.GA5847@lklug.pdn.ac.lk обсуждение исходный текст |
| Ответы |
Re: Group by, count, order by and limit
|
| Список | pgsql-hackers |
My 3rd attempt to post ...
Consider this query on a large table with lots of different IDs:
SELECT id FROM my_table GROUP BY id ORDER BY count(id) LIMIT 10;
It has an index on id. Obviously, the index helps to evaluate count(id)
for a given value of id, but count()s for all the `id's should be
evaluated, so sort() will take most of the time.
Is there a way to improve performance of this query? If not, please
give some indication to do a workaround on the source itself, so perhaps
I may be able to come out with a patch.
Thanks in advance.
Anuradha
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