Sql Query Order Problem

So I've got the follow model in activerecord, I will use Discussion.user_replied_group_discussions(@user)it returns the recent replied discussions alright, but how do I modify the

Solution 1:

This will order according to latest discussions.updated_at time:

where("discussable_type = 'Group' AND id IN (#{discussion_ids}) 
order by updated_at DESC ",

If you want to order by comment.created_at, use this query:

SELECT d.*
     , MAX(c.created_at) AS lastCommentTime
FROM discussions d
  JOIN comments c
    ON d.id = c.commentable_id
WHERE c.commentable_type = 'Discussion'AND c.user_id = userIDtoCheck
GROUPBY d.id
ORDERBY lastCommentTime DESC        <--- latest first