mysql - HAVING和GROUP BY一起使用时，SQL只做聚合吗？

Question

在下面的声明中:

SELECT CustomerID, Country
FROM Customers
GROUP BY Country
HAVING count(CustomerID)>7

我想返回具有 7 个以上客户 ID 的国家/地区的所有客户 ID。但它只为每个国家/地区返回 1 个 ID。

我需要执行以下操作才能获得我想要的内容:

SELECT CustomerID, Country
FROM Customers
WHERE Country in (SELECT Country FROM Customers GROUP BY Country HAVING COUNT(CustomerID)>7)

谁能解释一下为什么？

Answer 1

您可以将其很好地构造为子查询的连接:

SELECT CustomerID 
FROM Customers c
JOIN (
  SELECT Country 
  FROM Customers 
  GROUP BY Country 
  HAVING COUNT(CustomerID) > 7
) c2 on c.Country = c2.Country;