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From: Guillaume Cottenceau <gc@mnc.ch>
To: Michael Lewis <mlewis@entrata.com>
Cc: postgres performance list <pgsql-performance@postgresql.org>
Subject: Re: much slower query in production
References: <878skpnx0u.fsf@mnc.ch> <20200226162809.GZ31889@telsasoft.com>
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Date: Wed, 26 Feb 2020 20:37:48 +0100
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	(Michael Lewis's message of "Wed, 26 Feb 2020 11:18:53 -0700")
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Michael Lewis <mlewis 'at' entrata.com> writes:

>  UPDATE multicards
>  SET defacements = COALESCE( count, 0 )
>  FROM ( SELECT multicard_uid, COUNT(*) AS count FROM tickets GROUP BY multicard_uid ) AS sub
>  WHERE uid = multicard_uid OR multicard_uid is null;
>
> I expect this should work. Not sure of performance of course.

This looked great but as it seems you suspected, it's very slow :/
I interrupted it after 5 minutes run on my dev computer.

-- 
Guillaume Cottenceau