SQL给出了一个错误，即使看起来是正确的

Question

出现错误，我试图找出问题所在，但无济于事。请帮助

 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永远不会是NULL，则HAVING是多余的，因此也许就足够了：

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