MySQL - Count number of relating rows over multiple tables

Question

I am making a "quiz app". Each quiz have multiple questions (quizComponents), and each question has multiple answer options (quizComponentOptions) that the participant can select from. The answers are save in the quizResults table. I have these tables:

• Quiz( quizID, quizTitle );
• QuizComponents( componentId, quizID, quizQuestion );
• QuizComponentOptions( optionId, componentId, optionValue );
• QuizResults( resultId, personId, answerOptionId, componentId );
• CorrectOptions( componentId, optionId );

I would like to get a list of all quizes, with a total number of components in each quiz, and also number of correct / incorrect answers in each quiz for any given personId. Something like:

quizTitle   total_quiz_components   correct_answers     incorrect_answers   
"Quiz 1"            3                       2                   1
"Quiz 2"            10                      1                   9

The following query gives me all rows in Quiz, with the total number of quiz components every quiz contains.

SELECT q.quizTitle, count(qc.componentId) AS total_quiz_components FROM Quiz q
    LEFT JOIN QuizComponents qc ON qc.quizId=q.quizId
        GROUP BY q.quizId;

But then I'm stuck in this relations madness.

Answer 1

you need case based aggregation to get the correct and incorrect answers.

SELECT q.quizTitle, 
       count(qc.componentId) AS total_quiz_components ,
       sum ( case when CO.optionId = QR.answerOptionId then 1 else 0 end) as correct_answers,
       sum ( case when CO.optionId <> QR.answerOptionId then 1 else 0 end) as incorrect_answers,
FROM Quiz q
LEFT JOIN QuizComponents qc ON qc.quizId=q.quizId
LEFT JOIN QuizResults QR on 
QR.componentId = QC.componentId
LEFT JOIN CorrectOptions CO
on CO.componentId = QR.componentId
GROUP BY q.quizTitle;