分配值SQL

Question

我試圖找到一個更有效的方式來做到這一點，因爲我已經走了遊標路線，並且討厭我在SQL中使用遊標時遇到的性能問題。我試圖在有價值的物品之間分配付款，並跟蹤任何剩餘金額。例如...

Payments    
-------- 
10, 
20 

Items 
------ 
5, 
5, 
10 

實質上會返回第一個付款（10）適用於前兩個項目，並用盡。第二項付款（20）適用於第三項，剩下10項。我能夠使用遊標完成這項工作。只是好奇，如果有人對如何更有效地做到這一點有一些想法。

乾杯！

Answer 1

假設你有一組有序的ID爲支付和物品，你可以創建一個項目來支付的映射表，然後做這樣的事情（見http://sqlfiddle.com/#!3/4b6f8/4）：

-- Populate mapping table 
INSERT INTO PaymentsForItems (ItemID, PaymentID) 
SELECT ItemID, 
     (SELECT MIN(PaymentID) 
     FROM Payments p1 
     WHERE (SELECT SUM(ItemValue) 
       FROM Items i2 
       WHERE i2.ItemID <= i1.ItemID) <= 
       (SELECT SUM(PaymentValue) 
       FROM Payments p2 
       WHERE p2.PaymentID <= p1.PaymentID)) 
FROM Items i1; 

這並沒有顯示餘數 - 不知道你想如何表示這個，但可以很容易地分開插入一行（例如用NULL作爲ID）。

Answer 2

而不是光標，爲什麼你沒有得到你所有的物品和付款，並在你的代碼中工作？

它可能會更快，你將不得不擱置這2種方式。

在Java：

PreparedStatement psItems = con.prepareStatement("SELECT itemId,item FROM items"); 
PreparedStatement psPayments = con.prepareStatement("SELECT payId,payment FROM payments"); 
ResultSet rsItems = psItems.executeQuery(); 
ResultSet rsPayments = psPayments.executeQuery(); 

int currPaymentLeft = 0; 
int currentPayId = 0; 
int currentItemId = 0; 

while(rsItems.next()) { 
    int priceItem = rsItems.getInt("item"); 
    currentItemId = rsItems.getInt("itemId"); 
    if (currPayment < priceItem) { 
     // Here we are in the case where the last payment was over the items it bought. 
     // Except if currPayment is 0. In this case, there is no rest. 
     if (currPayment > 0) { 
      // This is the rest case 
      // In currentPayId, we have the Id of a Payment 
      // where there is currPayment left which will be unused. 
      // Do whatever you want with this Id and amount. 
     } 

     currPayment = 0; 
     while(rsPayments.next()) { 
      currPaymentLeft = rsItems.getInt("payment"); 
      int payId = rsItems.getInt("payId"); 
      if(payment >= priceItem) { 
       currPaymentLeft -= priceItem; 
       // Link currentPayId with currentItemId 
       // Create a query, store it in a collection, wo what you want. 

       // Get out of this while loop 
       break; 
      } 
      // else, the payment is less than the priceItem 
      // so this payment won't be of any use. 
      // This is a total rest case 
      // In currentPayId, we have the Id of a Payment 
      // where there is currPayment left which will be unused. 
      // Do whatever you want with this Id and amount. 
     } 
    } 
    else { 
     currPaymentLeft -= priceItem; 
     // Link currentPayId with currentItemId because itemId was paid with currentPayId 
    } 
} 

Answer 3

據我所知，你有兩個截然不同但相似的事件 - 收到新的付款，並創建一個新的成本項目。在每個時刻，您需要更新另一個表，因此看起來需要存儲過程或觸發器，具體取決於您的插入機制。

創建新項目時，您可以找到未付款項的最早付款，然後將其減少該項目的成本。

同樣，創建新付款時，您按順序分配金額（@amount）。

update items 
set 
    paid = 
     case when @amount>=runningTotal then items.amount 
     else 
      case when @amount - (runningTotal - (amount-paid))>0 
       then @amount - (runningTotal - (amount-paid)) 
       else 0 
      end 
     end   
from 
    items 
cross apply 
    (
     select sum(amount-paid) as runningTotal 
     from items 
     where id <= items.id 
    ) as rt 

（當然使用原子事務）

Answer 4

我測試了這段代碼與SQL Server 2005，並且它似乎確定。 希望它可以幫助一些。

WITH tItems 
AS 
(
SELECT A.ItemId, A.ItemValue, (SELECT COALESCE(SUM(B.ItemValue), 0) 
           FROM Items B 
           WHERE B.ItemId < A.ItemId) AS PrevItemTotal, 

           (SELECT COALESCE(SUM(C.ItemValue), 0) 
           FROM Items C 
           WHERE C.ItemId <= A.ItemId) AS CurrItemTotal 
FROM Items A 
), 
tPayments 
AS 
(
SELECT A.PaymentId, A.PaymentValue, (SELECT COALESCE(SUM(B.PaymentValue), 0) 
            FROM Payments B 
            WHERE B.PaymentId < A.PaymentId) AS PrevPaymentTotal, 

            (SELECT COALESCE(SUM(C.PaymentValue), 0) 
            FROM Payments C 
            WHERE C.PaymentId <= A.PaymentId) AS CurrPaymentTotal 
FROM Payments A 
), 
tDistribution 
AS 
(
SELECT *, 
CASE 
    WHEN PrevPaymentTotal - PrevItemTotal <= 0 THEN 
     CASE 
      WHEN PaymentValue - (PrevItemTotal-PrevPaymentTotal) <= ItemValue THEN PaymentValue - (PrevItemTotal-PrevPaymentTotal) 
      ELSE ItemValue 
     END 
    ELSE -- PrevPaymentTotal - PrevItemTotal > 0 
     CASE 
      WHEN ItemValue - (PrevPaymentTotal - PrevItemTotal) < PaymentValue THEN ItemValue - (PrevPaymentTotal - PrevItemTotal) 
      ELSE PaymentValue 
     END 
END AS Distribution 
FROM tItems X, tPayments Y 
WHERE Y.CurrPaymentTotal > X.PrevItemTotal AND Y.PrevPaymentTotal < X.CurrItemTotal 
) 

SELECT ItemId, ItemValue, PaymentId, PaymentValue, Distribution, 
ItemValue - SUM (Distribution) OVER (PARTITION BY ItemId) AS Remaining 
FROM tDistribution