select * into b from a where 1<>1
insert into b(a, b, c) select d,e,f from b;
select a.title,a.username,b.adddate from table a,(select max(adddate) adddate from table where table.title=a.title) b
select a.a, a.b, a.c, b.c, b.d, b.f from a LEFT OUT JOIN b ON a.a = b.c
select * from 日程安排 where datediff('minute',f开始时间,getdate())>5
delete from info where not exists ( select * from infobz where info.infid=infobz.infid )