select a.ID,a.USER,b.CL,PRI=sum(c.PRI)
from A表 as a
inner join B表 as b on a.ID=b.ID
inner join C表 as c on a.ID=c.ID
group by a.ID,a.USER,b.CL
from A表 as a
inner join B表 as b on a.ID=b.ID
inner join C表 as c on a.ID=c.ID
group by a.ID,a.USER,b.CL
select a.id,a.user,b.cl,sum(c.pri) from a inner join b on b.id=a.id inner join c on c.id=a.id group by a.id,a.user,b.cl