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From: Greg Sabino Mullane <htamfids@gmail.com>
Date: Thu, 12 Feb 2026 09:47:39 -0500
Message-ID: <CAKAnmmKfV4K6CfMuQkfQxccP0JRC5orV1tmaq8pB_+EdCZS1yw@mail.gmail.com>
Subject: Re: Guarantee order of batched pg_advisory_xact_lock
To: Nico Heller <nico.heller@posteo.de>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-general@postgresql.org
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On Thu, Feb 12, 2026 at 6:18=E2=80=AFAM Nico Heller <nico.heller@posteo.de>=
 wrote:

> I just checked for hash collisions with the following query today:
>
> SELECT COUNT(*), hashtextextended(key, 0) FROM
> (
>   SELECT key FROM table1
>   UNION
>

FWIW, you need UNION ALL, not UNION, if you are trying to detect duplicate
values (hashed or not) across tables.

Cheers,
Greg

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<div dir=3D"ltr"><div dir=3D"ltr">On Thu, Feb 12, 2026 at 6:18=E2=80=AFAM N=
ico Heller &lt;<a href=3D"mailto:nico.heller@posteo.de">nico.heller@posteo.=
de</a>&gt; wrote:</div><div class=3D"gmail_quote gmail_quote_container"><bl=
ockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-lef=
t:1px solid rgb(204,204,204);padding-left:1ex"><u></u>

 =20
   =20
 =20
  <div>
    <p>I just checked for hash collisions with the following query
      today:<br>
      <br>
      SELECT COUNT(*), hashtextextended(key, 0) FROM<br>
      (<br>
      =C2=A0 SELECT key FROM table1<br>
      =C2=A0 UNION=C2=A0</p></div></blockquote><div>=C2=A0</div><div>FWIW, =
you need UNION ALL, not UNION, if you are trying to detect duplicate values=
 (hashed or not) across tables.</div><div><br></div><div>Cheers,</div><div>=
Greg</div><div><br></div></div></div>

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