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
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TIP 5: don't forget to increase your free space map settings
