From: | Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com> |
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To: | Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> |
Cc: | pgsql-hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Fix optimization of foreign-key on update actions |
Date: | 2019-02-06 22:04:21 |
Message-ID: | c919566d-17ad-7a93-b3f2-7b64afc1297a@2ndquadrant.com |
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Lists: | pgsql-hackers |
On 06/02/2019 12:23, Andrew Gierth wrote:
> Two values which are sql-equal but not identical, such as two strings in
> a case-insensitive collation that differ only by case, are
> distinguishable in some contexts but not others, so what context
> actually applies to the quoted rule?
>
> I think the only reasonable interpretation is that it should use the
> same kind of distinctness that is being used by the unique constraint
> and the equality comparison that define whether the FK is satisfied.
By that logic, a command such as
UPDATE t1 SET x = '0' WHERE x = '-0';
could be optimized away as a noop, because in that world there is no
construct by which you can prove whether the update happened.
I think that would not be satisfactory.
--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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