通過在基礎顏色上添加列來計算庫存可用

Question

我正在嘗試計算sql中的庫存。我有4款產品，尺寸，購買和銷售。產品表

+----+------------------+ 
| id | product_name  | 
+----+------------------+ 
| 1 | apple   | 
|----|------------------| 
| 2 |banana   | 
|----|------------------| 
| 3 |mango    | 
+----+------------------+ 

現在顏色表

+----+------------------+ 
| id | color_name  | 
+----+------------------+ 
| 1 | dark   | 
|----|------------------| 
| 2 | light   | 
+----|------------------+ 

購表人是

+-------+-------------+ 
| id | quantity |color 
+-------+-------------+ 
| 1 | 15  |dark 
+-------+-------------+ 
| 1 | 10  |light 
+-------+-------------+ 
| 2 | 5   |dark 
+-------+-------------+ 
| 3 | 25  |light 
+-------+-------------+ 

，銷售表

+-------+-------------+ 
| id | quantity |color 
+-------+-------------+ 
| 1 | 5   |dark 
+-------+-------------+ 
| 1 | 5   |light 
+-------+-------------+ 
| 2 | 5   |dark 
+-------+-------------+ 
| 3 | 5   |light 
+-------+-------------+ 

採購和銷售表有外鍵ID引用產品表的ID。現在，我嘗試計算顏色的基礎上，購買和銷售以下形式的股票可即相差太大

+----+------------------+-------------+ 
| id | product_name  | quantity |color 
+----+------------------+-------------+ 
| 1 | apple   | 10  |dark 
|----|------------------|-------------| 
| 1 | apple   | 5  |light 
|----|------------------|-------------| 
| 2 |banana   | 0  |dark 
|----|------------------|-------------| 
| 3 |mango    | 20  |light 
+----+------------------+-------------+ 

我有以下腳本，我曾嘗試：

SELECT p.id, 
     p.Name, 
     Purchase.purchaseQty - sales.salseQty AS totalQty 

FROM Product p 
    OUTER APPLY (
     SELECT purchase.id, 
       SUM(purchase.quantity) purchaseQty 

     FROM purchase 
     WHERE purchase.id = p.id 
     GROUP BY 
      purchase.id 
) Purchase 
    OUTER APPLY (
     SELECT sales.id, 
       SUM(sales.quantity) salseQty 
     FROM sales 
     WHERE sales.id = p.id 
     GROUP BY 
      sales.id 
) sales 
; 

Answer 1

這應該解決問題：

select P.id, Pr.product_name, 
     case when S.quantity is null then P.quantity 
      else P.quantity - S.quantity end as quantity, 
     P.color from purchase as P 
left join sales AS S on (P.id = S.id and P.color = S.color) 
join product AS Pr on Pr.id = P.id