1
select XingM,KeM,ChengJ
from student
group by XingM,KeM,ChengJ
having count(*)>12
delete a
from student a
where id<>(select min(id) from student where XingM=a.XingM and KeM=a.KeM and ChengJ=a.ChengJ)
select XingM,KeM,ChengJ
from student
group by XingM,KeM,ChengJ
having count(*)>12
delete a
from student a
where id<>(select min(id) from student where XingM=a.XingM and KeM=a.KeM and ChengJ=a.ChengJ)
select * from student a,student b where a.XingM=b.XingM and a.KeM=b.KeM and a.ChengJ=b.ChengJ
delete a
from student a
where id not in (select min(id) from student where XingM=a.XingM and KeM=a.KeM and ChengJ=a.ChengJ)
delete student
where id not in(select min(id) from student group by kem having count(*)>1)
go
2
delete student
where id not in(select min(id) from student group by kem)
from student as a,(
select XingM,KeM,ChengJ
from student
group by XingM,KeM,ChengJ
having count(*)>1) as b
where a.XingM=b.XingM and a.KeM=b.KeM and a.ChengJ=b.ChengJ