mysql - SQL 给出错误，即使看起来是正确的

Question

报错，我试图看看哪里出了问题，但无济于事。请帮忙

 SELECT UserId, AVG(Total) AS AvgOrderTotal
FROM Invoices
HAVING COUNT(OrderId) >= 1

Answer 1

您缺少GROUP BY:

SELECT UserId, AVG(Total) AS AvgOrderTotal
FROM Invoices
GROUP BY UserId
HAVING COUNT(OrderId) >= 1

假设 OrderId 永远不会 NULL，则 HAVING 是多余的，所以也许这就足够了:

SELECT UserId, AVG(Total) AS AvgOrderTotal
FROM Invoices
GROUP BY UserId;