SQL（Sybase）返回計算行的總和

Question

以下查詢返回所有擁有貸方餘額（列ID和總計）的客戶 - 是否有任何方式只返回總計？

SELECT Customer_ID AS 'ID', 
    (
    SELECT SUM(Credit) - SUM(Debit) 
    FROM A_Sales_Ledger 
    WHERE Document_Date <= '2013-09-30' 
     AND Customer_ID = ID 
) AS 'Total' 
FROM A_Sales_Ledger 
WHERE Total > 0 
GROUP BY Customer_ID 

Answer 1

嘗試是這樣的：

SELECT SUM(a.total) 
FROM (
    SELECT (SUM(Credit) - SUM(Debit)) AS "total" 
    FROM A_Sales_Ledger 
    WHERE Document_Date <= '2013-09-30' 
    GROUP BY Customer_ID 
    HAVING SUM(Credit) - SUM(Debit) > 0 
) a; 

sqlfiddle demo