Question

I have two tables:

question
question_id | question

question_answer
answer_id | question_id | choice_id | user_id | explain

I want to get all questions for which particular user haven’t answered yet.

SELECT question, question_id as questionId 
FROM question q 
LEFT JOIN question_answer qa USING(question_id)
WHERE qa.user_id!=$userId

I get in this case zero rows. I tried also

SELECT question, q.question_id as questionId 
FROM question q 
LEFT JOIN question_answer qa ON q.question_id=qa.question_id AND qa.user_id!=$userId

Obviously this returns all records. I stuck here how to make this query.

Answer 1

The part of your LEFT JOIN where you check for a specific user should be reversed, i.e. user_id = $userId instead of user_id <> $userId.

From the resulting rows you select the ones where user_id IS NULL to find the questions for which $userId has not answered (yet).

SELECT question, q.question_id as questionId 
FROM question q 
LEFT JOIN question_answer qa ON q.question_id=qa.question_id AND qa.user_id=$userId
WHERE qa.user_id IS NULL