Horton

Re: BUG #19435: Error: "No relation entry for relid 2" Triggered by Complex Join with Self-Referencing Tables

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alexander Korotkov <aekorotkov@gmail.com>
Cc: Andrei Lepikhov <lepihov@gmail.com>, Kirill Reshke <reshkekirill@gmail.com>, Tender Wang <tndrwang@gmail.com>, Fujii Masao <masao.fujii@gmail.com>, ammmkilo@163.com, pgsql-bugs@lists.postgresql.org
Date: 2026-03-20T20:26:13Z
Lists: pgsql-bugs

Attachments

I wrote:
> At the very least we need to add comments, but I wonder if we
> don't actually need an Assert that ChangeVarNodesWalkExpression
> is not invoked directly on a Query.  It would have done the
> right thing before this patch, but now it won't.  That's an
> okay tradeoff for fixing the bare-Var case, but not documenting
> what you did is not okay.

After further contemplation I've decided that an Assert would be
wrong, because it's not impossible that a callback would want
to invoke this on a sub-Query --- for instance, if it wanted to
short-circuit ChangeVarNodes's processing of a SubLink node,
it would need to do that.  The key point is that if we do see a
Query node here, we will treat it as a sub-query not a top-level
query, which also justifies skipping the work that
ChangeVarNodesExtended does on a top-level Query.  So we just
need a comment explaining that.  I'm thinking about the attached.

(BTW, by this reasoning the previous implementation of
ChangeVarNodesWalkExpression was doubly wrong, since it would
have done the wrong thing at a Query node as well as a Var node.)

			regards, tom lane

Commits

  1. Further improve commentary about ChangeVarNodesWalkExpression()

  2. Improve commentary about ChangeVarNodesWalkExpression().

  3. Fix self-join removal to update bare Var references in join clauses

  4. Implement Self-Join Elimination