From: | Joe Love <joe(at)primoweb(dot)com> |
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To: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Feature request: optimizer improvement |
Date: | 2013-10-31 16:04:57 |
Message-ID: | CAK3BLoSan3o2a9kLVDetkor-zyqn-1jmc0Y-rPtiS9a+uFL-uA@mail.gmail.com |
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Lists: | pgsql-hackers |
In postgres 9.2 I have a function that is relatively expensive. When I
write a query such as:
select expensive_function(o.id),o.* from offeirng o where valid='Y' order
by name limit 1;
the query runs slow and appears to be running the function on each ID,
which in this case should be totally unnecessary as it really only needs to
run on 1 row.
When I rewrite the query like so:
select expensive_function(o.id), o.*
from (select *offering where valid='Y' order by name limit 1) o;
the expensive function only runs once and thus, much faster. I would think
that the optimizer could handle this situation, especially when limit or
offset is used and the expensive function is not used in a group by, order
by or where.
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