Info 表
id,ClassId,Product
1 1 AAA
2 1 BBB
3 2 CCC
4 3 DDDClass 表
ClassId ,ClassName
1 T-1
2 T-2
3 F-1要求得到如下结果:ClassName TotalNum
T-1 2
T-2 1
F-1 1
id,ClassId,Product
1 1 AAA
2 1 BBB
3 2 CCC
4 3 DDDClass 表
ClassId ,ClassName
1 T-1
2 T-2
3 F-1要求得到如下结果:ClassName TotalNum
T-1 2
T-2 1
F-1 1
from Class a
TotalNum=(select count(*) from info where ClassID=C.ClassID group by ClassId)
from Class C
Select
A.ClassName,
Count(B.id) As TotalNum
From Class A
Inner Join Info B
On A.ClassId=B.ClassId
from class c left join info i
on c.classid=i.classid
group by c.ClassName
from class as a,info as b
where a.ClassId = b.ClassId
group by a.ClassName,a.ClassId