Function reconsider_outer_join_clause

src/backend/optimizer/path/equivclass.c:2079–2198

* reconsider_outer_join_clauses for a single LEFT/RIGHT JOIN clause * * Returns true if we were able to propagate a constant through the clause. */

 * Returns true if we were able to propagate a constant through the clause.
 */
static bool
reconsider_outer_join_clause(PlannerInfo *root, RestrictInfo *rinfo,
							 bool outer_on_left)
{
	Expr	   *outervar,
			   *innervar;
	Oid			opno,
				collation,
				left_type,
				right_type,
				inner_datatype;
	Relids		inner_relids,
				inner_nullable_relids;
	ListCell   *lc1;

	Assert(is_opclause(rinfo->clause));
	opno = ((OpExpr *) rinfo->clause)->opno;
	collation = ((OpExpr *) rinfo->clause)->inputcollid;

	/* If clause is outerjoin_delayed, operator must be strict */
	if (rinfo->outerjoin_delayed && !op_strict(opno))
		return false;

	/* Extract needed info from the clause */
	op_input_types(opno, &left_type, &right_type);
	if (outer_on_left)
	{
		outervar = (Expr *) get_leftop(rinfo->clause);
		innervar = (Expr *) get_rightop(rinfo->clause);
		inner_datatype = right_type;
		inner_relids = rinfo->right_relids;
	}
	else
	{
		outervar = (Expr *) get_rightop(rinfo->clause);
		innervar = (Expr *) get_leftop(rinfo->clause);
		inner_datatype = left_type;
		inner_relids = rinfo->left_relids;
	}
	inner_nullable_relids = bms_intersect(inner_relids,
										  rinfo->nullable_relids);

	/* Scan EquivalenceClasses for a match to outervar */
	foreach(lc1, root->eq_classes)
	{
		EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
		bool		match;
		ListCell   *lc2;

		/* Ignore EC unless it contains pseudoconstants */
		if (!cur_ec->ec_has_const)
			continue;
		/* Never match to a volatile EC */
		if (cur_ec->ec_has_volatile)
			continue;
		/* It has to match the outer-join clause as to semantics, too */
		if (collation != cur_ec->ec_collation)
			continue;