Question

我在尝试从下表中计算累积组得分时遇到错误：

group_details:
id      name
=====================
1       Group 1
2       Group 2
3       Group 3

group_members:
id      group_id  
======================
1       1           
2       1           
3       2       
4       2       
5       3     

answers:
id      member_id   is_correct      
=================================
1       1           1        
2       1           0      
3       2           1          
4       2           1         
5       3           1          
6       3           0
7       4           0          
8       4           1

我正在努力实现这一目标：

Group Name            Total Members     Total Score (%)
==============================================
Group 1                  2              75.00
----------------------------------------------
Group 2                  2              50.00
---------------------------------------------- 
Group 3                  1              0
----------------------------------------------

运行查询时，返回空结果。请在下面查看我的代码。

 SELECT 
    ((SUM(a.is_correct) / (2 * SUM(m.id))) * 100)  as cummulative_score,
    SUM(m.id) as total_members,
    g.name
  FROM
    `group_details` AS g 
    LEFT JOIN `group_members` m 
      ON m.group_id = g.id
    LEFT JOIN `answers` a 
      ON a.member_id = m.id 
  WHERE a.is_correct = 1
  GROUP BY g.id;

Answer 1

此查询将为您提供所需的结果。请注意，根据您问题中的表名，我已使用answers作为答案表，如果它实际上称为answer，则需要更改该JOIN。

SELECT 
    g.name,
    COUNT(DISTINCT m.id) AS `Total Members`,
    ROUND(COALESCE(AVG(a.is_correct), 0) * 100, 2) AS `Total Score (%)`
  FROM
    `group_details` AS g 
    LEFT JOIN `group_members` m 
      ON m.group_id = g.id
    LEFT JOIN `answers` a 
      ON a.member_id = m.id 
  GROUP BY g.id

输出：

name        Total Members   Total Score (%)     
Group 1     2               75.00
Group 2     2               50.00
Group 3     1               0.00

Answer 2

将“ LEFT JOIN答案a”更改为“ LEFT JOIN答案a”，它应该可以工作。

我还建议您避免使用别名，因为将临时表重命名为“ a”，“ g”之类的东西并没有任何好处，这对每个人来说确实很令人困惑，并且使调试/分析查询变得非常困难。另外，您应该使用MySQL客户端向您突出显示此类错误，例如MySQL Workbench或类似的内容。

MYSQL加入3个表格并计算累积百分比

2 个答案: