左连接，分组和计数所需的数组

Question

I have questions, answers, question_type and possible_answers tables. A question has a lot of answers which can be, in example, 1-5 stored in possible_answers table and related through the question_type table and questions table.

I usually solve this making a sql that returns the possible answers and then in a for I look again of every for with more sql sentences... that takes a lot of time. My idea is to make in a single sql an array with the count of the answers of a question that puts zero on the possible_answers that has no answers:

answer | count

1 | 234  
2 | 123    
3 | 0    
4 | 0    
5 | 876    

Is it possible? thanks a lot!

Answer 1

I am assuming that the answer table contains a foreign key questionID. I will also assume that the question type is unnecessary to join them, but acts as a lookup table.

If you want to populate a possible_answers table with the count of answers to questions, including zeros, try

INSERT INTO possible_answers
SELECT questions.questionID, COUNT(answers.answerID)
FROM questions
LEFT JOIN answers
ON questions.questionID = answers.questionID
GROUP BY questions.questionID;