如何在 MySQL 中按两列比较两个查询？

Question

按两列比较两个查询的最佳方法是什么？这些是我的表格：

此表显示考试问题

idEvaluation | Question | AllowMChoice | CorrectAnswer|
1                1            0             3 
1                2            1             4
1                2            1             5
1                3            0             9

此表显示已完成的考试

  idExam| idEvaluation | Question | ChosenAnswer|
    25        1              1            2
    25        1              2            4
    25        1              2            5
    25        1              3            8      

我必须计算正确答案的百分比，考虑到某些问题可能允许多项选择。

正确答案/总答案 * 100

感谢您的提示！

Answer 1

此代码将向您显示问题列表以及是否正确回答了这些问题。

select
    A.Question,
    min(1) as QuestionsCount,
    -- if this evaluates to null, they got A) the answer wrong or B) this portion of the answer wrong
    -- we use MIN() here because we want to mark multi-answer questions as wrong if any part of the answer is wrong. 
    min(case when Q.idEvaluation IS NULL then 0 else 1 end) as QuestionsCorrect
from
    ExamAnswers as A
    left join ExamQuestions as Q on Q.Question = A.Question and Q.CorrectAnswer = A.ChosenAnswer
group by
    A.Question -- We group by question to merge multi-answer-questions into 1

已确认输出：

注意，这些列有意以这种方式命名，因为它们将作为子查询包含在内在下面的第 2 部分中。

---

此代码将为您提供测试分数。

select
    sum(I.QuestionsCorrect) as AnswersCorrect,
    sum(I.QuestionsCount) as QuestionTotal,
    convert(float,sum(I.QuestionsCorrect)) / sum(I.QuestionsCount) as PercentCorrect -- Note, not sure of the cast-to-float syntax for MySQL
from
    (select
        A.Eval,
        A.Question,
        min(1) as QuestionsCount,
        min(case when Q.idEvaluation IS NULL then 0 else 1 end) as QuestionsCorrect
    from
        ExamAnswers as A
        left join ExamQuestions as Q on Q.Question = A.Question and Q.CorrectAnswer = A.ChosenAnswer
    where 
        A.Eval = 25
    group by
        A.Question, A.Eval) as I
group by        
    I.Eval

输出已确认：

这将传达一般概念。您的列名称 idEvaluation 和 Eval 对我来说很难理解，但我确信您可以调整上面的代码以适合您的目的。

请注意，我在 sql server 中执行此操作，但我使用了相当基本的 SQL 功能，因此它应该可以很好地转换为 MySQL。