客户姓名显示涉及平均值的问题

Question

我正在尝试编写一个 SQL 查询来显示总购买量大于所有购买的平均购买量的客户姓名。

我尝试使用下面的代码，但出现错误。

SELECT C.FirstName
FROM CUSTOMERS as C
JOIN ORDERS AS O ON C.CustomerID = O.CustomerID
GROUP BY O.CustomerID
HAVING O.TotalPaid < Avg(O.TotalPaid);

这是错误：

Error Code: 1054. Unknown column 'O.TotalPaid' in 'having clause'

Answer 1

您似乎有两个错误：

1. 您应该将

   O.TotalPaid

   包含到

   SUM

   中，因为

   HAVING

   应包含聚合数据
2. 您应该对平均值进行子查询以保持其恒定。

查询应该是这样的：

SELECT C.FirstName
FROM CUSTOMERS as C
JOIN ORDERS AS O ON C.CustomerID = O.CustomerID
GROUP BY O.CustomerID
HAVING SUM(O.TotalPaid) < (SELECT AVG(TotalPaid) FROM ORDERS);

另一个可能的选择应该包括在

SELECT

SUM(O.TotalPaid)

中，如下所示：

SELECT C.FirstName, SUM(O.TotalPaid)
FROM CUSTOMERS as C
JOIN ORDERS AS O ON C.CustomerID = O.CustomerID
GROUP BY O.CustomerID
HAVING SUM(O.TotalPaid) < (SELECT AVG(TotalPaid) FROM ORDERS);