Function targetIsInSortList

src/backend/parser/parse_clause.c:3813–3834

* targetIsInSortList * Is the given target item already in the sortlist? * If sortop is not InvalidOid, also test for a match to the sortop. * * It is not an oversight that this function ignores the nulls_first flag. * We check sortop when determining if an ORDER BY item is redundant with * earlier ORDER BY items, because it's conceivable that "ORDER BY * foo USING <, foo USING <<<" is no

 * is that a TLE might be in only one of the lists.
 */
bool
targetIsInSortList(TargetEntry *tle, Oid sortop, List *sortList)
{
	Index		ref = tle->ressortgroupref;
	ListCell   *l;

	/* no need to scan list if tle has no marker */
	if (ref == 0)
		return false;

	foreach(l, sortList)
	{
		SortGroupClause *scl = (SortGroupClause *) lfirst(l);

		if (scl->tleSortGroupRef == ref &&
			(sortop == InvalidOid ||
			 sortop == scl->sortop ||
			 sortop == get_commutator(scl->sortop)))
			return true;
	}
	return false;
}

/*
 * findWindowClause