mysql - 选择具有差异的对象

Question

我试图找到一种方法来运行它:

SELECT 
    s.system_number,
    s.total_points,
    p.licensed_points,
    SUM(p.licensed_points) - SUM(s.total_points) AS difference_points
FROM 
    server AS s 
    LEFT JOIN 
        practice AS p ON p.system_number = s.system_number 
WHERE 
    difference_points < 0

我的目标是只选择 difference_points < 0 的对象

有人知道怎么做吗？

谢谢

Answer 1

• 在没有Group By 的情况下使用聚合函数Sum() 在这里没有意义。您需要对 s.system_number 进行Group By。
• 然后，您可以使用Having子句来考虑difference_points小于0的情况。

请尝试以下操作:

SELECT 
    s.system_number,
    SUM(s.total_points),
    SUM(p.licensed_points),
    SUM(p.licensed_points) - SUM(s.total_points) AS difference_points
FROM 
    server AS s 
    LEFT JOIN 
        practice AS p ON p.system_number = s.system_number 
GROUP BY 
  s.system_number 
HAVING 
    difference_points < 0