mysql - 关联子查询mysql

Question

所以我有一张产品表

Product ID | Product Name
===========+===============
1          | Tissues
2          | Glass

我有一张销售表

Sale ID    | Product ID | Quantity | Price
===========+============+==========+=============
1          | 1          | 1        | 55
2          | 2          | 1        | 60

我有一张购买表

Batch ID | Total Value | Quantity | Product ID
=========+=============+==========+==================
1        | 100         | 100      | 1
2        | 10          | 50       | 2
3        | 1           | 1        | 2

所以我尝试使用查询根据平均成本计算利润

SELECT tblsale.product_id, 
       tblproduct.product_name, 
       SUM(tblsale.`quantity`) qty,
       SUM(tblsale.`Price`*tblsale.`quantity`) sales, 
       (SELECT sum(total_value) / sum(quantity) VWAP 
        FROM tblpurchases 
        WHERE product_id = tblsale.product_id) average_price, 
       (average_price * qty) cost, 
       (sales-cost) profit 
FROM   tblsale, tblproduct 
WHERE tblproduct.product_id = tblsale.`product_id` 
GROUP by tblsale.`product_id`

但我似乎无法让它工作，我得到的“平均价格”是一个未知列，我该如何正确构建查询

Answer 1

SQL 不支持在同一 SELECT 子句中引用列别名 - 这就是您的 average_price 列返回 1054 错误的原因。您要么必须在子选择、派生表/内联 View 中执行您需要的任何操作，要么在必要时重用底层逻辑。这是逻辑重用的示例:

   SELECT prod.product_id, 
          prod.product_name, 
          SUM(s.quantity) qty,
          SUM(s.Price * s.quantity) sales, 
          SUM(pur.total_value) / SUM(pur.quantity) average_price, 
          SUM(pur.total_value) / SUM(pur.quantity) * SUM(s.quantity) cost, 
          SUM(s.Price * s.quantity) - (SUM(pur.total_value) / SUM(pur.quantity) * SUM(s.quantity)) profit 
     FROM tblproduct prod 
LEFT JOIN tblsale s ON prod.product_id = s.product_id
LEFT JOIN tblpurchases pur ON pur.product_id = prod.product_id
 GROUP BY s.product_id

我的查询使用的是 ANSI-92 JOIN 语法，我建议您的查询使用 ANSI-89 语法。参见 this question for more details .