一列的总和与另一列的计数之比

Question

I'm trying to count the number of passed quizzes, as per the following results table:

So, we have 3 quizzes, and if the proportion of correct answers is >= 0.5, then it is passed. If the answer is correct, the result column shows 1, otherwise it shows 0.

For example, quiz 1 has 5 questions, of which 3 are correct. Quiz 2 has 3 questions, of which 1 is correct. Quiz 3 has 2 questions, both are correct.

So, this user has passed 2 quizzes out of 3.

My expected result is: "2 quizzes out of 3 are passed." using MYSQL with PHP with something like:

$number_of_quizzes = 'SELECT COUNT(DISTINCT quiz_id) FROM TABLE'

But, I'm struggling with the query to count the number of rows in the 'result' column and the sum of its values - per quiz.

Is this possible to do with MYSQL alone, or should the logic be transferred to PHP? How?

Can anyone help?

Answer 1

Try this:

$quiz_list = 'SELECT DISTINCT quiz_id FROM TABLE'
$count = 0
$number_of_quizzes = 'SELECT COUNT(DISTINCT quiz_id) FROM TABLE'

foreach ($quiz as &$quiz_list) {
    $nb_quiz = 'SELECT COUNT(*) FROM TABLE WHERE quiz_id = ' . $quiz . '';
    $nb_correct = 'SELECT COUNT(*) FROM TABLE WHERE quiz_id = ' . $quiz . ' AND result = 1';
    $count += ($nb_correct / $nb_quiz > 0.5 ? 1 : 0);
}
$expected_result = $count . " quizzes out of " . $number_of_quizzes . " are passed.";

Of corse you have to change my SQL queries in string to real queries.