MYSQL Query that get different values using a condition

i was looking for something like this:

• forum_reply (id, Text, Data, Post, User)


• forum_post (id, Title, Text, Section, Data, User)

Post, User and Section are foreign keys.

I would show all the posts, of the section that i'm in (i'll use a WHERE Section = '".$_GET['section']."' , i'm working with PHP), order by the data, but:

• If the post hasen't got replys, order THAT post using data of the post


• If the post has more then 0 replys, order THAT post using data of the LAST reply

My final result would be a table that have all the posts rows order by the data that i specified first. Like this:

• POST 1 | 0 Reply | Data of post: 19/12/2014 13:00 -> Take Data of the post


• POST 2 | Reply > 0, Data of the last reply: 19/12/2014 14:00 -> Take Data of the last reply


• ecc..

After that, display all such as:

• POST 2 (19/12/2014 14:00)


• POST 1 (19/12/2014 13:00)

I really can't made that; really need you help! Thanks very much.