Question

id  name    gpa  batch
1   jhon    2    y1
2   sandy   2.8  y2
4   kile    3    y2
5   siya    3.2  y1

我想找到最大平均gpa的批次。所以我写了下面的代码。

select max(gpa)
from student
where gpa in (select batch,AVG(gpa)
              from student
              group by batch)

我通过单独执行它检查子查询，它工作正常。但主查询中有错误。

Answer 1

您可以改为使用TOP：

SELECT TOP 1 batch
FROM student
GROUP BY batch
ORDER BY AVG(gpa) DESC

DEMO

使用MAX：

SELECT *
FROM(
    SELECT batch, avg_gpa = AVG(gpa)
    FROM student
    GROUP BY batch
) s
WHERE avg_gpa = (
    SELECT MAX(avg_gpa)
    FROM (
        SELECT batch, avg_gpa = AVG(gpa)
        FROM #student
        GROUP BY batch
    ) t
)

Answer 2

您的子查询返回2个值，主查询中的In函数正在查找1个项目。我建议从内部查询中删除批处理。

Answer 3

SELECT TOP 1 batch, avg_gpa = AVG(gpa)
FROM   student
GROUP BY batch
ORDER BY avg_gpa desc

子查询和聚合函数

3 个答案: