Message-ID: <52e52bddd9d5396ca07f103f799518f82e2c8aad.camel@cybertec.at>
Subject: Re: BUG #18173: ERROR:  could not identify a comparison function
 for type unknown
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: 409800246@qq.com, pgsql-bugs@lists.postgresql.org
Date: Tue, 31 Oct 2023 12:10:05 +0100
In-Reply-To: <18173-c971c32eb961e810@postgresql.org>
References: <18173-c971c32eb961e810@postgresql.org>
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On Mon, 2023-10-30 at 13:24 +0000, PG Bug reporting form wrote:
> PostgreSQL version: 16.0
>=20
> postgres=3D# CREATE TABLE test_v(id int,name varchar(30));
> CREATE TABLE
> postgres=3D# insert into test_v values(9,'abc'),(9,'def'),(9,'gh'),
> (9,'gh');
> INSERT 0 4
> postgres=3D# explain (costs off) select distinct
> (id,name,'D3Q84xpymM',123,'123') from test_v;
>                          QUERY PLAN                         =20
> -------------------------------------------------------------
>  Unique
>    ->  Sort
>          Sort Key: (ROW(id, name, 'D3Q84xpymM', 123, '123'))
>          ->  Seq Scan on test_v
> (4 rows)
>=20
> postgres=3D# select distinct (id,name,'D3Q84xpymM',123,'123') from test_v=
;
> ERROR:  could not identify a comparison function for type unknown

This is not a bug.  You probably want to remove the parentheses.

Yours,
Laurenz Albe