Question

I have 2 tables:

The question table with the following structure:

id
title
userid
date

and answers table with the following structure:

id
idquestion
userid
message
date

I want to show all the questions and the latest answer to that question.

For example, if we have 5 questions, I would like to get something like this:

id    title   message   messagedate
1     qs 1    mess 1    2010-11-18
2     qs 2    mess 2    2010-11-19
3     qs 3    mess 3    2010-11-20
4     qs 4    mess 4    2010-11-21

My query so far:

    SELECT q.id, qa.id as answerid, title, qa.message 
      FROM `questions` q 
INNER JOIN questions_answers qa 
        ON q.id = qa.idquestion 
  GROUP BY q.id 
  ORDER BY q.id, answerid DESC

But it doesn’t work correctly, it groups by the question id(removing all the other columns messages, leaving only the first message – so the order by is useless)

Any help appreciated. Thanks

Answer 1

The old problem. Here’s the solution:
http://dev.mysql.com/doc/refman/5.1/en/example-maximum-column-group-row.html

In your case:

SELECT q.id, qa.id as answerid, title, qa.message 
FROM questions q
JOIN questions_answers qa ON q.id = qa.idquestion
LEFT JOIN questions_answers qa2 ON qa.idquestion = qa2.idquestion AND qa.date < qa2.date
WHERE qa2.idquestion IS NULL

(The idea is to split the problem in two operations: One join from questions to answers and then use the methods from the MySQL article.)