Question

我有一个基于用户的基础上的一堆课程分数

------------------------
|uid |lesson_id |score |
------------------------
|1   |0         |20    |
|1   |0         |25    |
|1   |0         |15    |
|1   |0         |40    |
|1   |1         |70    |
|1   |0         |10    |
|1   |1         |20    |
|1   |1         |55    |
|1   |1         |55    |
|1   |0         |5     |
|1   |2         |65    |
------------------------

我还有一张可以得分的所有课程表：

------------
|lesson_id |
------------
|0         |
|1         |
|2         |
|3         |
|4         |
|5         |
------------

我需要根据第一张表中的分数计算第二张表中每节课的最高分数，并取第二张表中课程数的平均值：

因此，分数表的最高分数是（对于用户1）：

-----------------------
|lesson_id |max_score |
-----------------------
|0         |40        |
|1         |70        |
|2         |65        |
-----------------------

我需要总结一下：175并除以表2中的课程总数：6应给出答案29.16

任何想法如何在一个声明中做到这一点？

我可以得到得分表（对于用户1）的所有最大值的平均值，如下所示：

SELECT AVG(max_score) AS avg_max_score FROM 
(
    SELECT uid, lesson_id, MAX(score) AS max_score FROM cdu_user_progress 
    AND uid =1
    GROUP BY lesson_id 
) AS m

Answer 1

SELECT
    AVG(max_score)
FROM
   (

    SELECT
         lesson.lesson_id,
         max(isNull(score,0)) as max_score
    FROM
         lesson
    LEFT JOIN
         cdu_user_progress
    ON
         lesson.lesson_id = cdu_user_progress.lesson_id
    GROUP BY
         lesson.lesson_id
   ) AS m

SQL：需要从一个表中获取MAX值并除以另一个表中的总行数

1 个答案: