Function build_expression_pathkey

src/backend/optimizer/path/pathkeys.c:1110–1148

* build_expression_pathkey * Build a pathkeys list that describes an ordering by a single expression * using the given sort operator. * * expr, nullable_relids, and rel are as for make_pathkey_from_sortinfo. * We induce the other arguments assuming default sort order for the operator. * * Similarly to make_pathkey_from_sortinfo, the result is NIL if create_it * is false and the express

 * is false and the expression isn't already in some EquivalenceClass.
 */
List *
build_expression_pathkey(PlannerInfo *root,
						 Expr *expr,
						 Relids nullable_relids,
						 Oid opno,
						 Relids rel,
						 bool create_it)
{
	List	   *pathkeys;
	Oid			opfamily,
				opcintype;
	int16		strategy;
	PathKey    *cpathkey;

	/* Find the operator in pg_amop --- failure shouldn't happen */
	if (!get_ordering_op_properties(opno,
									&opfamily, &opcintype, &strategy))
		elog(ERROR, "operator %u is not a valid ordering operator",
			 opno);

	cpathkey = make_pathkey_from_sortinfo(root,
										  expr,
										  nullable_relids,
										  opfamily,
										  opcintype,
										  exprCollation((Node *) expr),
										  (strategy == BTGreaterStrategyNumber),
										  (strategy == BTGreaterStrategyNumber),
										  0,
										  rel,
										  create_it);

	if (cpathkey)
		pathkeys = list_make1(cpathkey);
	else
		pathkeys = NIL;

	return pathkeys;
}

/*
 * convert_subquery_pathkeys