Re: Fix optimization of foreign-key on update actions

From: Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>
To: Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>
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 09:11:13
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Andrew Gierth wrote:
> SQL2016, 15.17 Execution of referential actions
> 10) If a non-null value of a referenced column RC in the referenced
> table is updated to a value that is distinct from the current value
> of RC, then,
> [snip all the stuff about how ON UPDATE actions work]
> does that "is distinct from" mean that IS DISTINCT FROM would be true,
> or does it mean "is in some way distinguishable from"? Nothing I can see
> in the spec suggests the latter.

My 2003 standard defines, and even condescends to be informal: distinct (of a pair of comparable values): Capable of being distinguished within a given context.
Informally, not equal, not both null. A null value and a non-null value are distinct.

Laurenz Albe

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