SQL语句

　　描述：exhibitiononline表主键exhiid， exhibitor表有外键 exhid，对应表 exhibitiononline的主键exhiid;

　　exhibitiononline表---------> 一对多 <------------- exhibitor表

　　功能：查询出 exhibitiononline表中，exhiid存在于表 exhibitor中的所有数据，并根据 exhibitor表的exhid的数量排序

　　select * from exhibitiononline join

　　(select exhid,count(exhid) as s from exhibitor group by exhid) as t

　　on exhibitiononline.exhiid=t.exhid

　　order by t.s desc