Date: Tue, 14 Oct 2025 17:46:23 +0200
From: hubert depesz lubaczewski <depesz@depesz.com>
Sender: depesz@depesz.com
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: order by alias - doesn't work sometimes?
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On Tue, Oct 14, 2025 at 11:10:31AM -0400, Tom Lane wrote:
> ORDER BY output-column-alias is a messy hangover from SQL92.
> In later SQL versions, identifiers in ORDER BY have the same
> interpretation as in WHERE and other clauses, namely they are
> columns sourced by the FROM clause.  Supporting both interpretations
> makes for a lot of ambiguity, so we only allow the old interpretation
> in exactly the case required by SQL92, namely "ORDER BY identifier".
> 
> This is documented ...

Well, now I understand this:

>> Each expression can be the name or ordinal number of an output column
>> (SELECT list item), or it can be an arbitrary expression formed from
>> input-column values.

better. Thanks.

Best regards,

depesz