如何在单个查询中计算每个用户的百分比？

Question

我进行查询，显示每个用户回答每个部门的问题数量，以及每个用户在回答该部门的问题时的错误百分比。

所以，我尝试这样的查询，

SELECT  d.department_id, d.department_name as department, 
        a.username, COUNT(a.username)total,
        (  (COUNT(r.is_correct)*100) / 
              (   SELECT COUNT(a.username) total
                  FROM qa_report r
                  LEFT JOIN tbl_user a ON (r.user_id = a.admin_id)
                  LEFT JOIN department d on (a.department_id = d.department_id)
                  WHERE d.department_name = 'Dept1' AND is_correct='yes'
              )
        ) as correct_percent
FROM qa_report r
LEFT JOIN tbl_user a ON (r.user_id = a.admin_id)
LEFT JOIN department d on (a.department_id = d.department_id)
WHERE d.department_name = 'Dept1'
GROUP BY a.username

这是结果，

total列是用户为该部门回答的问题回答的数量。

在此total中，正确且错误的答案正在混合。

但是当我尝试计算每个部门的正确/不正确的百分比时，correct_percent列仍然是错误的。

问题出在这一行，

(  (COUNT(r.is_correct)*100) / 
          (   SELECT COUNT(a.username) total
              FROM qa_report r
              LEFT JOIN tbl_user a ON (r.user_id = a.admin_id)
              LEFT JOIN department d on (a.department_id = d.department_id)
              WHERE d.department_name = 'Dept1' AND is_correct='yes'
          )
    ) as correct_percent

我需要在这个地方获得每个用户的正确百分比，

(correct percent of answer*100)/total question that user answer eg. John => total: 10, correct 5, incorrect 5, correct %=50%

我非常感谢任何建议。

Answer 1

我现在可以解决这个问题。当我尝试计算百分比时，我错了。 这是有效的查询，

SELECT  d.department_id, d.department_name as department, 
    a.username, COUNT(a.username)total,
    (  (COUNT(CASE WHEN r.is_correct='yes' THEN 1 END)*100) / ( COUNT(a.username)) ) as correct_percent,
    (  (COUNT(CASE WHEN r.is_correct='no' THEN 1 END)*100) / ( COUNT(a.username)) ) as incorrect_percent
FROM qa_report r
LEFT JOIN tbl_user a ON (r.user_id = a.admin_id)
LEFT JOIN department d on (a.department_id = d.department_id)
WHERE d.department_name = 'Dept1'
GROUP BY a.username

希望对某人有所帮助。