Question

执行选择后，我收到错误＆＃34;未知列＆＃39;点＆＃39;在＆＃39; where子句＆＃39;

如何从外部查询中删除包含从子查询返回的空记录的行？（我需要使用子查询，因为我需要运行另一组子查询来返回我之后的结果）

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

我也尝试过，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

提前致谢

解决方案：

我所寻找的是 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

问题是您无法在SELECT子句中使用WHERE别名，它们必须位于HAVING。

但是如果使用内连接，则首先不会获得任何空行。

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

当子查询返回null时删除外部查询上的行

1 个答案: