Question

执行查询时：

SELECT DISTINCT (u.name),u.class,
(SELECT ( markscored) FROM marklist WHERE subject LIKE 'biology' AND u.id=m.id) AS biology,
(SELECT ( markscored) FROM marklist WHERE subject LIKE 'chemistry' AND u.id=m.id) AS chemistry,
(SELECT ( markscored) FROM marklist WHERE subject LIKE ' physics' AND u.id=m.id) AS physics,
(SELECT SUM( markscored) FROM marklist WHERE u.id=m.id) AS TOTAL,
(SELECT SUM(outof) FROM marklist WHERE u.id=m.id) AS OUTOF,


((SELECT SUM( markscored) FROM marklist WHERE u.id=m.id)/(SELECT SUM(outof) FROM marklist WHERE u.id=m.id)*100) as percentage
FROM  u, marklist m
WHERE u.id=m.userid

我收到的错误是：

错误1242（21000）：子查询返回超过1行

我该如何解决这个问题？

Answer 1

以下可能对您有所帮助。除数不能为0，因此使用NULLIF将其更改为NULL。

    SELECT  u.name,u.class,
       SUM( markscored) AS TOTAL,
       SUM(outof) AS OUTOF
       SUM(CASE WHEN subject LIKE 'biology' THEN markscored ELSE 0 END) AS biology,
       SUM(CASE WHEN subject LIKE 'chemistry' THEN markscored ELSE 0 END) AS chemistry,
       SUM(CASE WHEN subject LIKE 'physics' THEN markscored ELSE 0 END) AS physics,
       SUM( markscored)/NULLIF(SUM(outof),0) as percentage

    FROM  u, marklist m
    WHERE u.id=m.userid
    GROUP BY u.name,u.class

查询更正w

1 个答案: