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help / color / mirror / Atom feedFrom: Andrei Lepikhov <[email protected]>
To: Frits Jalvingh <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: Question about nested loops..
Date: Fri, 10 Oct 2025 11:28:44 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAKhTGFW-KL0Fz8z5HrORtLh8YG1as=P1LZhG84U-HQ+ca77Azg@mail.gmail.com>
References: <CAKhTGFURW_AvZgWR20x-kWfSeGts=OWcuOnanhM-dwU9RjiRPw@mail.gmail.com>
<[email protected]>
<CAKhTGFW-KL0Fz8z5HrORtLh8YG1as=P1LZhG84U-HQ+ca77Azg@mail.gmail.com>
On 10/10/2025 10:51, Frits Jalvingh wrote:
> Hi Andrei,
> Thanks a lot for your response. I do not fully get it though because the
> well-performing query also references the outer (external?) relation:
> -> where eenheid.id_h_eenheid = eenheid_s.id_h_eenheid
> But your response made me think a but more.This is the schema of EXPLAIN for the second 'optimal' query:
Seq Scan on s_h_eenheid_ssm D
SubPlan 2
-> Hash Join
Hash Cond: (A.x = B.x)
-> Seq Scan on A
Filter: ...
-> Hash
-> Hash Join
Hash Cond: (C.y = B.x)
-> Seq Scan on s_h_huurovereenkomst_ssm C
-> Hash
-> Seq Scan on s_h_eenheid_ssm B
There is no reference to the upper relation D - each HashJoin refers to
its left and right side only.
-- regards, Andrei Lepikhov, pgEdge
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