http://blog.youkuaiyun.com/black0591/article/details/7027166
select count(distinct pur_ins_id), pur_ins_id, pur_ins_name from ias_placard_ins_puritem where supp_id =#{suppId}
and release_date > #{dateTime} and pur_ins_name is not null
group by pur_ins_id
order by release_date desc limit 20