public inbox for [email protected]  

help / color / mirror / Atom feed

From: Tom Lane <[email protected]>
To: David Rowley <[email protected]>
Cc: Chengpeng Yan <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Subject: Re: [PATCH] Fix hashed ScalarArrayOp semantics for NULL LHS with non-strict comparators
Date: Mon, 20 Apr 2026 00:14:03 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAApHDvr7K+Wu+ECgmZw057Mb1H6H87+ZWETHi28Ez_ALBKgmQA@mail.gmail.com>
References: <[email protected]>
	<CAApHDvoLFhtAFSwJdjsBcs9L4J4SzE09gkHLr9nJSGSj1CBaRw@mail.gmail.com>
	<CAApHDvr7K+Wu+ECgmZw057Mb1H6H87+ZWETHi28Ez_ALBKgmQA@mail.gmail.com>

David Rowley <[email protected]> writes:
> I've attached a version that "probes" the equality function for its
> NULL = NULL behaviour and its NULL = non-NULL behaviour and returns
> whatever the result of the probe was at the appropriate time.

> What I came up with does feel quite elaborate, so I'd quite like a 2nd opinion.

> The patch does assume that the non-strict function will return the
> same thing for NULL = non-NULL as it will for non-NULL = NULL.

Meh.  I think we assume that hashable equality functions satisfy the
symmetric law, ie A = B if and only if B = A, so that part is fine.
However, I do not care for the assumption that any random non-null
input will produce the same answer.  As a quick counter-example,
consider a text-like datatype that tries to emulate Oracle's semantics
that an empty string is the same as NULL.  Your code would arrive at
different results depending on whether the first non-null input
chanced to be an empty string.

(I've not read this whole thread, so I don't have a global opinion
on what we ought to do here.  I suspect it's a tricky subject.)

			regards, tom lane

view thread (11+ messages)  latest in thread

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected], [email protected]
  Subject: Re: [PATCH] Fix hashed ScalarArrayOp semantics for NULL LHS with non-strict comparators
  In-Reply-To: <[email protected]>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox