On Tue, Sep 19, 2017 at 7:31 PM, monika yadav <monika.1234ya...@gmail.com>
wrote:
> Hi All,
>
> I didn't understand why same sub plan for the sub query executed two
> times? As per the query it should have been executed only once.
>
> Can someone please explain this behaviour of query execution ?
>
The sum_bid at the end of the query is an alias for the entire subselect,
so it not entirely surprising that it gets interpolated twice. it is just
kind of unfortunate from a performance perspective.
The query I originally gave is equivalent to this query:
select
aid,
(select sum(bid) from pgbench_branches
where bbalance between -10000-abalance and 1+abalance
) as sum_bid
from pgbench_accounts
where aid between 1 and 1000
group by aid
having (select sum(bid) from pgbench_branches where bbalance
between -10000-abalance and 1+abalance ) >0;
In my originally query I just wrapped the whole thing in another select, so
that I could use the alias rather than having to mechanically repeat the
entire subquery again in the HAVING section. They give identical plans.
Cheers,
Jeff
