Right now, I am having trouble getting the planner to optimize queries
in the form of
select t.key, t.field from t a
where
(
select count(*) from t b
where b.field > a.field
) = k
The subplan (either index or seq. scan) executes once for each row in t,
which of course takes forever.
This query is a way of achieving LIMIT type results (substitute n-1
desired rows for k) using standard SQL, which is desirable in some
circumstances. Is it theoretically possible for this to be optimized?
Merlin
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