Function GetSortDetails

pg_documentdb/src/opclass/index_support.c:2681–2868

static List *
GetSortDetails(PlannerInfo *root, Index rti,
			   bool *hasOrderBy, bool *hasGroupby, bool *isOrderById)
{
	List *sortDetails = NIL;
	ListCell *sortCell;
	foreach(sortCell, root->query_pathkeys)
	{
		PathKey *pathkey = (PathKey *) lfirst(sortCell);
		if (pathkey->pk_eclass == NULL ||
			list_length(pathkey->pk_eclass->ec_members) != 1)
		{
			return NIL;
		}

		EquivalenceMember *member = linitial(pathkey->pk_eclass->ec_members);

		if (!IsA(member->em_expr, FuncExpr))
		{
			return NIL;
		}

		FuncExpr *func = (FuncExpr *) member->em_expr;
		if (func->funcid == BsonOrderByFunctionOid())
		{
			if (*hasGroupby)
			{
				break;
			}

			*hasOrderBy = true;
		}
		else if (EnableOrderByIndexTerm &&
				 (func->funcid == BsonOrderByIndexFunctionOid() ||
				  func->funcid == BsonOrderByIndexReverseFunctionOid()))
		{
			/* TODO: Collation index pushdown support. */
			if (*hasGroupby)
			{
				break;
			}

			*hasOrderBy = true;
		}
		else if (func->funcid == BsonExpressionGetFunctionOid() ||
				 func->funcid == BsonExpressionGetWithLetFunctionOid())
		{
			if (*hasOrderBy)
			{
				return NIL;
			}

			*hasGroupby = true;
		}
		else if (func->funcid == DocumentDBCoreBsonToBsonFunctionOId())
		{
			Expr *firstArg = linitial(func->args);
			if (!IsA(firstArg, FuncExpr))