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Simplify restriction matching in self-join elimination.

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In match_unique_clauses(), use equal() to compare complete restriction
clauses after substituting the relation ID, instead of comparing their
operands separately.  This ensures that the operator and input
collation also match, preventing incorrect self-join elimination when
restrictions have identical operands but different semantics.

The former code apparently intended to support matching clauses to
commuted versions of those clauses, but the amount of complication
that added seems far out of proportion to the value, so just drop
that goal.  (If we wanted to reinstate it, something based on
applying CommuteOpExpr or equivalent logic would be better.)

Author: Tender Wang <tndrwang@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAHewXNmwYrp0DTuisCyfXXjVa_irUdDFApUzLVDg3J4MAR6gEg@mail.gmail.com
Backpatch-through: 18
This commit is contained in:
Tom Lane
2026-10-15 12:42:34 -04:00
parent 931ce42ef9
commit 8f2b598b4b
1 changed files with 12 additions and 36 deletions
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48
src/backend/optimizer/plan/analyzejoins.c
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@@ -1718,57 +1718,33 @@ split_selfjoin_quals(PlannerInfo *root, List *joinquals, List **selfjoinquals,
}
/*
* Check for a case when uniqueness is at least partly derived from a
* baserestrictinfo clause. In this case, we have a chance to return only
* one row (if such clauses on both sides of SJ are equal) or nothing (if they
* are different).
* Check that each base restriction used to prove uniqueness of relid has
* a matching restriction in outer->baserestrictinfo, after replacing
* relid with outer->relid.
*
* Require equal() clauses, including the operator and input collation.
* Formerly this tried to match commuted forms of clauses, but that added
* a great deal of extra complication without much extra value.
*/
static bool
match_unique_clauses(PlannerInfo *root, RelOptInfo *outer, List *uclauses,
Index relid)
{
Assert(outer->relid > 0 && relid > 0);
foreach_node(RestrictInfo, rinfo, uclauses)
{
Expr *clause;
Node *iclause;
Node *c1;
bool matched = false;
Assert(outer->relid > 0 && relid > 0);
/* Only filters like f(R.x1,...,R.xN) == expr we should consider. */
Assert(bms_is_empty(rinfo->left_relids) ^
bms_is_empty(rinfo->right_relids));
/* Convert the clause from uclauses to use outer's Vars */
clause = (Expr *) copyObject(rinfo->clause);
ChangeVarNodes((Node *) clause, relid, outer->relid, 0);
iclause = bms_is_empty(rinfo->left_relids) ? get_rightop(clause) :
get_leftop(clause);
c1 = bms_is_empty(rinfo->left_relids) ? get_leftop(clause) :
get_rightop(clause);
/*
* Compare these left and right sides with the corresponding sides of
* the outer's filters. If no one is detected - return immediately.
*/
/* Look for a matching restriction on the outer relation */
foreach_node(RestrictInfo, orinfo, outer->baserestrictinfo)
{
Node *oclause;
Node *c2;
if (orinfo->mergeopfamilies == NIL)
/* Don't consider clauses that aren't similar to 'F(X)=G(Y)' */
continue;
Assert(is_opclause(orinfo->clause));
oclause = bms_is_empty(orinfo->left_relids) ?
get_rightop(orinfo->clause) : get_leftop(orinfo->clause);
c2 = (bms_is_empty(orinfo->left_relids) ?
get_leftop(orinfo->clause) : get_rightop(orinfo->clause));
if (equal(iclause, oclause) && equal(c1, c2))
if (equal(clause, orinfo->clause))
{
matched = true;
break;