>>>Does it know that the input to the sort routine is already sorted and
>>>hence is a no-op?
>
>>Yes
>
> No, but in most cases this will use an index and hence will assume that
> the index is responsible for ordering.
OK, so what's going on here?
usa=> explain select * from users_myfoods_map where user_id=1 and
date='2003-11-03' order by date; QUERY PLAN
-------------------------------------------------------------------------------------------------------------------
Sort (cost=4.84..4.85 rows=2 width=22) Sort Key: date -> Index Scan using users_myfoods_map_user_id_date_key on
users_myfoods_map (cost=0.00..4.83 rows=2 width=22) Index Cond: ((user_id = 1) AND (date =
'2003-11-03'::date))
(4 rows)
(That's on our enormous live table)
Chris