关于COUNT的简单问题(是Pradox的)
三个表 a,b,c
a是主表,b和c都是子表
a b c (表名)
---------------------------------
SN SN Detail SN Detail (字段名)
------------------------------------------
1 1 fdf 2 gfgdg
2 1 342 3 dfsdfs
3 2 ewrew 3 fdsfsdf
怎么得出
SN count(b) count(c)
--------------------
1 2 0
2 0 1
3 0 2
我写的是
Select a.sn,count(b.sn), count(c.sn)
from a left join b on a.sn=b.sn
left join c on a.sn=c.sn
group by a.sn
结果是错误的.请大家指点.....