Question

There is a scenario. There is an ask-and-answer website. An answerer can modify his answer, and the history of modification is saved on the server. Be default, only the latest version of each answer is displayed.

select * from answers where questionid='$questionid' group by answerer_id 

So I can group all answers by answerer, then I need to select the latest version of each subgroup. How to achieve this?

Answer 1

The GROUP BY clause seems to just use the first available row, so you could try using a sub-query to re-arrange them so the latest answer is on top.

SELECT * 
FROM (
    SELECT * FROM `answers`
    WHERE questionid='$questionid'
    ORDER BY answerer_id DESC
) as `dyn_answers` 
GROUP BY answerer_id