select top 10 ----distinct
title,id from messages
where posttype = '求购'
group by title,id
order by min(posttime) desc --order by posttime desc
title,id from messages
where posttype = '求购'
group by title,id
order by min(posttime) desc --order by posttime desc
(
select distinct title,id from messages where posttype = '求购' group by title,id order by posttime desc
) a