MySQL查询减法值

Question

我有这个问题：

SELECT (
        SELECT purchase_code 
        FROM qa_suppliers_invoices a 
        WHERE a.supplier_invoice_code = b.item_invoicecodesupplier
       ) AS purchase_code, 
      item_code, 
      status_code, 
      itempurchase_quantity, 
      item_costprice 
FROM qa_items_purchases b
ORDER BY purchase_code LIMIT 0,20000;

返回以下数据

我希望像使用（item_code）行的紫色颜色一样进行GROUP，我想添加所有（itempurchase_quantity）制作对（status_code）行的引用然后应用这个ecuation（status_15 - status_16）也像图像一样。

我想要这个结果，GROUP（）：

purchase_code  item_code  status_code  itempurchase_quantity  item_costprice
1              1506       15           713                    126.94
2              1503       16           12                     0.00
2              1683       15           9                      25.28
2              1931       15           60                     0.00

在item_code（1997）的情况下，不存在status_code = 15因此返回一个负数（-9），然后你不需要显示。

2              2325       16           50                     849.97

注意： 我需要消失所有16 status_code

Demo data to play with query at sqlfiddle

更新 这是一张详细说明我需要的照片：

Answer 1

SELECT 
      a.purchase_code,
      b.item_code, 
      '15' AS status_code,
      SUM(
        CASE b.status_code 
            WHEN 15 THEN b.itempurchase_quantity
        ELSE 
            - (b.itempurchase_quantity) 
        END) 
        AS itempurchase_quantity,
      b.item_costprice
FROM qa_items_purchases b
    INNER JOIN qa_suppliers_invoices a 
        ON a.supplier_invoice_code = b.item_invoicecodesupplier
GROUP BY purchase_code, b.item_code, b.item_costprice
    HAVING itempurchase_quantity > 0
    ORDER BY purchase_code 
    LIMIT 0,20000

Answer 2

使用此

SELECT purchase_code, item_code, status_code, 
     SUM(case status_code 
         when 15 then itempurchase_quantity
         ELSE (-1*itempurchase_quantity) END
        ) AS itempurchase_quantity
FROM myTable
GROUP BY purchase_code;

Demo

注意

您需要使用自己的数据，而不是myTable。我创建了myTable，其中包含您在图片中显示的数据。

我认为新的查询将是

SELECT (
    SELECT purchase_code 
    FROM qa_suppliers_invoices a 
    WHERE a.supplier_invoice_code = b.item_invoicecodesupplier
   ) AS purchase_code, 
  item_code, 
  status_code, 
  SUM(case status_code 
         when 15 then itempurchase_quantity
         ELSE (-1*itempurchase_quantity) END
        ) AS itempurchase_quantity, 
  item_costprice 
FROM qa_items_purchases b
GROUP BY purchase_code
ORDER BY purchase_code 
LIMIT 0,20000;

---

更新1

SELECT purchase_code, item_code, status_code, 
       SUM(case status_code 
           when 15 then itempurchase_quantity
           ELSE (-1*itempurchase_quantity) END
          ) AS itempurchase_quantity
FROM myTable
GROUP BY purchase_code, item_code;

New Demo