SQL：需要另一個表來獲得從一個表，然後除以MAX值按行的總數

Question

我有上課了一堆成績表，在用戶通過用戶基礎

------------------------ 
|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 | 
------------------------ 

我也有所有可能的教訓表可以砍下：

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

我需要計算在從第一表格中的分數第二個表中的每一課的最高得分，並利用這一平均在第二個表中的課程數量：

所以，最大得分的得分表是（用於用戶1）：

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

我需要它們求和：通過吸取總數表175和除法2：6，其應該給回答29.16

任何想法如何在單個語句中做到這一點？

我可以得到的分數表（用戶1）所有的MAX值的平均值，像這樣：

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