Function make_pathkeys_for_sortclauses

src/backend/optimizer/path/pathkeys.c:1655–1684

* make_pathkeys_for_sortclauses * Generate a pathkeys list that represents the sort order specified * by a list of SortGroupClauses * * The resulting PathKeys are always in canonical form. (Actually, there * is no longer any code anywhere that creates non-canonical PathKeys.) * * We assume that root->nullable_baserels is the set of base relids that could * have gone to NULL below the So

 * 'tlist' is the targetlist to find the referenced tlist entries in
 */
List *
make_pathkeys_for_sortclauses(PlannerInfo *root,
							  List *sortclauses,
							  List *tlist)
{
	List	   *pathkeys = NIL;
	ListCell   *l;

	foreach(l, sortclauses)
	{
		SortGroupClause *sortcl = (SortGroupClause *) lfirst(l);
		Expr	   *sortkey;
		PathKey    *pathkey;

		sortkey = (Expr *) get_sortgroupclause_expr(sortcl, tlist);
		Assert(OidIsValid(sortcl->sortop));
		pathkey = make_pathkey_from_sortop(root,
										   sortkey,
										   root->nullable_baserels,
										   sortcl->sortop,
										   sortcl->nulls_first,
										   sortcl->tleSortGroupRef,
										   true);

		/* Canonical form eliminates redundant ordering keys */
		if (!pathkey_is_redundant(pathkey, pathkeys))
			pathkeys = lappend(pathkeys, pathkey);
	}
	return pathkeys;
}

/****************************************************************************
 *		DISTRIBUTION KEYS