Re: SELECT performance drop

On Wed, 2019-01-23 at 10:28 -0700, Jan Nielsen wrote:
> select
> order0_.id as id1_7_,
> order0_.created_by as created_2_7_,
> order0_.created_date as created_3_7_,
> order0_.last_modified_by as last_mod4_7_,
> order0_.last_modified_date as last_mod5_7_,
> order0_.consumer as consumer6_7_,
> order0_.market_id as market_14_7_,
> order0_.original as original7_7_,
> order0_.owner_id as owner_i15_7_,
> order0_.owner_target as owner_ta8_7_,
> order0_.price as price9_7_,
> order0_.session_id as session16_7_,
> order0_.side as side10_7_,
> order0_.supplier as supplie11_7_,
> order0_.type as type12_7_,
> order0_.units as units13_7_
> from
> fm_order order0_ cross
> join
> fm_session session1_
> where
> order0_.session_id=session1_.id
> and order0_.type='LIMIT'
> and session1_.original=7569
> and (
> order0_.consumer is null
> or order0_.consumer>0
> and (
> exists (
> select
> 1
> from
> fm_order order2_ cross
> join
> fm_session session3_
> where
> order2_.session_id=session3_.id
> and order2_.id=order0_.consumer
> and session3_.original=7569
> and order2_.type='LIMIT'
> and order2_.owner_id<>order0_.owner_id
> )
> )
> )
> order by
> order0_.last_modified_date DESC;

It might be more efficient to rewrite that along these lines:

SELECT DISTINCT order0_.*
FROM fm_order order0_
JOIN fm_session session1_ ON order0_.session_id = session1_.id
LEFT JOIN fm_order order2_ ON order2_.id = order0_.consumer
LEFT JOIN fm_session session3_ ON order2_.session_id = session3_.id
WHERE coalesce(order2_.id, 1) > 0
AND /* all the other conditions */;

Yours,
Laurenz Albe
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