删除行时，子查询返回null

Question

选择执行后，我收到了错误“未知列‘点’在‘where子句’

如何从包含空外部查询中删除行记录从子查询返回？（我需要使用子查询，因为我有需要运行到返回结果子查询的另一帮我后）

SELECT 
    s.student_name_first, 
    s.student_name_last, 
    (
    SELECT sum(i.points) 
    FROM incidents i 
    WHERE i.student = s.id 
    ) AS points 
FROM students s 
WHERE points IS NOT NULL 
GROUP BY s.id 

我也曾尝试，结果相同

SELECT 
    s.student_name_first, 
    s.student_name_last, 
    (
    SELECT sum(i.points) AS points 
    FROM incidents i 
    WHERE i.student = s.id AND points IS NOT NULL 
    ) AS p 
FROM students s 
GROUP BY s.id 

在此先感谢

---

解决方案：

我一直在寻找的是HAVING

SELECT 
    s.student_name_first, 
    s.student_name_last, 
    (
    SELECT COALESCE(sum(i.incident_points),0) 
    FROM incidents i 
    WHERE i.student = s.id 
    ) as points 
FROM students s 
GROUP BY s.id 
HAVING points > 0 

Answer 1

的问题是，你不能WHERE子句中使用别名SELECT，他们必须在HAVING。

但是，如果您使用内部联接，您将不会首先获得任何空行。

SELECT s.student_name_first, 
     s.student_name_last, 
     SUM(i.points) AS points 
FROM students s 
JOIN incidents i 
ON i.student = s.id 
GROUP BY s.id