Question

当尝试在FROM子句中运行嵌套子查询时，我偶然发现了MySQL（v.8）的奇怪行为。我正在使用的示例数据库的（相关部分）架构如下：

以下两个查询在SQL Server上运行相同：

SELECT SUM(tot) as total
 FROM (
     SELECT 
        SUM(OD.quantityOrdered * OD.priceEach) as tot,
        C.customerNumber
     FROM customers C
     INNER JOIN orders O ON C.customerNumber = O.customerNumber
     INNER JOIN orderdetails OD ON O.orderNumber = OD.orderNumber
     GROUP BY O.orderNumber, C.customerNumber
) AS CO
GROUP BY CO.customerNumber;

和

SELECT 
  (
    SELECT SUM(tot) as total
    FROM 
        (
            SELECT 
                (
                    SELECT  SUM(OD.quantityOrdered * OD.priceEach)
                    FROM orderdetails OD 
                    WHERE OD.orderNumber = O.orderNumber
                ) AS tot
            FROM orders O
            WHERE O.customerNumber = C.customerNumber
        ) AS ORD
  ) AS total
FROM customers AS C;

但是，在MySQL上，第一个运行正常，而第二个则导致错误：

Error Code: 1054. Unknown column 'C.customerNumber' in 'where clause'

我会感激有关为什么发生这种情况的任何线索。 请注意，我最感兴趣的不是解决此查询的方法或其他方法，而是了解嵌套查询失败的原因。

Answer 1

C表别名不在suquery的范围内
尝试使用连接重构查询

例如

select  c.customerNumber,  t.my_tot 
FROM customers AS C
INNER JOIN (

  SELECT  O.customerNumber, SUM(OD.quantityOrdered * OD.priceEach) my_tot
  FROM orderdetails OD 
  INNER JOIN orders O ON  OD.orderNumber = O.orderNumber
  GROUP BY O.customerNumber
) t on t.customerNumber = c.customerNumber

或

select  t.my_tot 
FROM customers AS C
INNER JOIN (

  SELECT  O.customerNumber, SUM(OD.quantityOrdered * OD.priceEach) my_tot
  FROM orderdetails OD 
  INNER JOIN orders O ON  OD.orderNumber = O.orderNumber
  GROUP BY O.customerNumber
) t on t.customerNumber = c.customerNumber

Answer 2

您可以尝试以下操作

SELECT 
  (   
      select SUM(tot) as total from

          (   
            SELECT 
                (
                    SELECT  SUM(OD.quantityOrdered * OD.priceEach)
                    FROM orderdetails OD 
                    WHERE OD.orderNumber = O.orderNumber
                ) AS tot,customerNumber
            FROM orders O
           )  as ord      
            WHERE ord.customerNumber = C.customerNumber        
  ) AS total
FROM customers AS C;

您的客户表不在条件WHERE O.customerNumber = C.customerNumber中使用的子查询范围内，因此我为此设置了别名然后在更高级别上，我使用相同的条件，其中客户表具有范围

Answer 3

在第二种情况下，您具有相关的子查询。但是，相关子句的深度为两个级别。

即使嵌套多个级别，许多数据库仍然可以识别c。但是，MySQL（以及Oracle和我认为MS Access）是一个将关联子句限制在一个层次上的数据库。

FROM子句中的子查询在MySQL中失败

3 个答案: