On 11/5/2011 4:11 PM, Tom Lane wrote:
Cstdenis<lists@xxxxxxxxxxx> writes:
If I understand that you are proposing as
select * from
(select distinct on (user_id) * from stories as s order
by user_id) as foo
order by date_submitted desc limit 10;
No, you always need to sort by *more* columns than are listed in
DISTINCT ON. That's what determines which row is picked in each
DISTINCT group. Read the SELECT reference page's example of how
to use DISTINCT ON.
regards, tom lane
Thanks. I was missing the obvious. This seems to give the results I need.
It's a shame the query parser isn't able to simply internally process
the query like that -- doing a second sort pass after the distinct
automatically in the case of the sort being on a different column from
distinct (instead of producing an error).
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