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From: Ashutosh Bapat <[email protected]>
To: Ewan Young <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: [email protected]
Subject: Re: GRAPH_TABLE: lateral reference with label disjunction fails with "plan should not reference subplan's variable"
Date: Thu, 4 Jun 2026 15:25:05 +0530
Message-ID: <CAExHW5vKmi_jMvd-OmG8OHytifQp0oKWP4p55FPCfL9V5Qn1Sg@mail.gmail.com> (raw)
In-Reply-To: <CAON2xHOYJ+dGZznY+oPyBHdLfRtzThQid5iEc-HOxODs3pb3AA@mail.gmail.com>
References: <CAON2xHOYJ+dGZznY+oPyBHdLfRtzThQid5iEc-HOxODs3pb3AA@mail.gmail.com>

Hi Ewan,
Thanks for trying out SQL/PGQ and the report.

On Thu, Jun 4, 2026 at 1:58 PM Ewan Young <[email protected]> wrote:
>
> Hi hackers,
>
> While testing with master I ran into an internal error in the
> SQL/PGQ code (commit 2f094e7ac69).  A lateral reference into a
> GRAPH_TABLE clause whose graph pattern contains a label disjunction
> resolving to more than one element table fails at plan time:
>
>     CREATE TABLE v1 (id int);
>     CREATE TABLE v2 (id int);
>     CREATE TABLE x (a int);
>     CREATE PROPERTY GRAPH g
>       VERTEX TABLES (v1 KEY (id) LABEL l1, v2 KEY (id) LABEL l2);
>
>     SELECT 1 FROM x,
>       GRAPH_TABLE (g MATCH (s IS l1|l2 WHERE s.id = x.a) COLUMNS (s.id));
>     ERROR:  plan should not reference subplan's variable
>
> The same pattern with a single label works fine, as does a label
> disjunction without the lateral reference.  Reproduces on any build of
> master and 19beta1; the equivalent hand-written query (LATERAL over a
> UNION ALL) plans fine.
>
> The cause is in rewriteGraphTable.c.  replace_property_refs_mutator()
> increments varlevelsup of lateral references by one, assuming the path
> query will directly become the GRAPH_TABLE's subquery.  That holds for
> a single path query, but when the disjunction produces several path
> queries, generate_union_from_pathqueries() wraps them in subquery RTEs
> of a new UNION query, one level deeper, and nothing compensates for
> that.  The planner then attributes the parameters to the wrong query
> level, which finalize_plan() detects.
>
> The attached patch increments the level of outer references in each
> path query once more at the point where they are wrapped in the UNION
> query, using IncrementVarSublevelsUp().  With the fix, the query above
> returns the same results as the hand-written UNION ALL equivalent.
>
> make check passes with the patch applied.

This bug is the same as the one being discussed in [1]. Let's continue
the discussion there.

[1] http://postgr.es/m/[email protected]

-- 
Best Wishes,
Ashutosh Bapat

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