急求一个复杂的SQL语句！！！

[Lamya]

select a.oilNum,sum(b.vol),sum(c.vol),sum(d.watervol),sum(e.watervol)
from newjr a left outer join Getin b
on a.oilNum=b.oilNum
left outer join GetOut c
on a.oilNum=c.oilNum
left outer join water d
on a.oilNum=d.oilNum and d.state=1
left outer join water e
on a.oilNum=e.oilNum and e.state=0
where a.gsid=1 group by a.oilNum
go
就是从三个表里面查出的数据汇总在一起，为什么聚合函数的运算结果增长了好几倍？
刚两个表的外联接就没问题？
请教这是哪里出了问题？