From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Michael Paquier <michael@paquier.xyz>
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: SIMILAR TO expressions translate wildcards where they shouldn't
Date: Tue, 27 May 2025 23:39:02 +0200
Message-ID: <b4b25c91f05f0be8fb7072c8dbf9d4ca6062b303.camel@cybertec.at> (raw)
In-Reply-To: <1101508.1748357652@sss.pgh.pa.us>
References: <16ab039d1af455652bdf4173402ddda145f2c73b.camel@cybertec.at>
<aC_K7JPXF0AdPZqB@paquier.xyz>
<aC_p7b5H6pLICU_e@paquier.xyz>
<5498224d1d5a6a3be7f29ae7725f76162d48372f.camel@cybertec.at>
<aDVUWaoZg8cW3B9x@paquier.xyz>
<37584c1321b984a0c5c05d213ef70b869d95a12a.camel@cybertec.at>
<1101508.1748357652@sss.pgh.pa.us>
On Tue, 2025-05-27 at 10:54 -0400, Tom Lane wrote:
> Laurenz Albe <laurenz.albe@cybertec.at> writes:
> > On Tue, 2025-05-27 at 14:57 +0900, Michael Paquier wrote:
> > > With some tweaks and the tests reworked, I am finishing with the
> > > reviewed version attached. What do you think?
>
> > Thank you; I think that is good to go.
>
> Code changes look good, but I think the test cases are too cute:
>
> +EXPLAIN (VERBOSE, COSTS OFF) SELECT (SELECT '') SIMILAR TO '_[_[:alpha:]_]_';
> + QUERY PLAN
> +---------------------------------------------------------------
> + Result
> + Output: ((InitPlan 1).col1 ~ '^(?:.[_[:alpha:]_].)$'::text)
> + InitPlan 1
> + -> Result
> + Output: ''::text
> +(5 rows)
>
> This will break whenever somebody decides it's worth optimizing
> a sub-select that looks like that. I'd suggest following the
> pattern
>
> explain (costs off) select * from text_tbl where f1 similar to 'z';
> QUERY PLAN
> ----------------------------------
> Seq Scan on text_tbl
> Filter: (f1 ~ '^(?:z)$'::text)
> (2 rows)
>
> which is both less noisy and less likely to change in future.
That's a good point.
I originally considered EXPLAIN (GENERIC_PLAN), but that would only
backpatch so far.
Yours,
Laurenz Albe
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To: pgsql-bugs@postgresql.org
Cc: laurenz.albe@cybertec.at, tgl@sss.pgh.pa.us, michael@paquier.xyz, pgsql-bugs@lists.postgresql.org
Subject: Re: SIMILAR TO expressions translate wildcards where they shouldn't
In-Reply-To: <b4b25c91f05f0be8fb7072c8dbf9d4ca6062b303.camel@cybertec.at>
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