From: Tom Lane <tgl@sss.pgh.pa.us>
To: 253540651@qq.com
cc: pgsql-bugs@lists.postgresql.org,
        Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Subject: Re: BUG #17318: ERROR: AddressSanitizer: SEGV on unknown address in
 optimizer
In-reply-to: <17318-2eb65a3a611d2368@postgresql.org>
References: <17318-2eb65a3a611d2368@postgresql.org>
Comments: In-reply-to PG Bug reporting form <noreply@postgresql.org>
	message dated "Mon, 06 Dec 2021 06:40:39 +0000"
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Date: Mon, 06 Dec 2021 09:56:40 -0500
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PG Bug reporting form <noreply@postgresql.org> writes:
>  WITH RECURSIVE x ( x ) AS ( SELECT 1 UNION ALL SELECT x FROM LATERAL ( (
> SELECT * FROM ( ( SELECT 4 AS x ) UNION ALL ( SELECT 5 AS x ) ) AS x WHERE x
> BETWEEN 1 AND 2 AND x < ( SELECT 3 GROUP BY DISTINCT ROLLUP ( x , x ) ,
> ROLLUP ( x , x ) ) ) UNION ALL ( SELECT ( SELECT x LIMIT 1 ) FROM x OFFSET 0
> LIMIT 5 ) ) AS x GROUP BY ROLLUP ( ( x , x , x ) , ( ( SELECT TRIM (
> TRAILING ' ' FROM SUBSTRING ( VERSION ( ) FROM '^[^0-9]*' ) ) WHERE ( x IS
> NOT NULL ) ) , x ) ) ) CYCLE x SET BOOLEAN USING VALUES SELECT FROM x GROUP
> BY DISTINCT CUBE ( x , x , x ) ;

I simplified this to

WITH RECURSIVE x ( x ) AS
  ( SELECT 1
    UNION ALL
    SELECT x FROM
    (
      SELECT 4 AS x
      UNION ALL
      SELECT x FROM x
    ) AS x
  )
CYCLE x SET b USING v
SELECT * FROM x
;

and now I'm not sure whether to consider this an optimizer bug
or failure to detect an unsupported case.  Our SELECT ref page
says

    Both the SEARCH and the CYCLE clause are only valid for recursive WITH
    queries. The with_query must be a UNION (or UNION ALL) of two SELECT
    (or equivalent) commands (no nested UNIONs).

This WITH query sure looks like nested UNIONs to me, so either
that restriction is stated incorrectly, or it's being enforced
inadequately.  If the former, we have an optimizer problem.

			regards, tom lane