left join on 多表同表不同条件

SQL code

sql="select a.ID as DID,"    sql=sql&" IsNull(sum(b.Signing_AmountIN),0) as q1a,"    sql=sql&" IsNull(sum(c.Signing_AmountIN),0) as q2a"    sql=sql&" from KL_Depart as a"        sql=sql&" left join KL_Signing b"    sql=sql&" on b.DepartID = a.ID"    sql=sql&" and b.Signing_Stage = 3 and b.UnitID = "&KL_UnitID&" and b.Signing_UseDate between '"&CDate(BDate)&"' and '"&CDate(BDate2)&"'"        sql=sql&" left join KL_Signing c"    sql=sql&" on c.DepartID = a.ID"    sql=sql&" and c.Signing_Stage = 3 and c.UnitID = "&KL_UnitID&" and c.ISCheckD = 1 and c.Signing_UseDate between '"&CDate(BDate)&"' and '"&CDate(BDate2)&"'"        sql=sql&" where a.UnitID  ="&KL_UnitID&" and a.ISWriteOFF = 0"    sql=sql&" group by a.ID"    sql=sql&" order by q1a desc"

如果我只Left join 一个的话，结果是正确的，但是我再增加了一个Left Join的话，结果q1a是正确结果的2倍，q2a是正确结果的3倍，请指点一下。

[解决办法]
两种解决办法:
1.先将表两两连接,然后再将连接结果连接:
select * from(
select ... from .. a left join ... b on a.id=b.id
)a inner join (
select ... from ...a left join ... b on a.id=b.id
)b on a.id=b.id
2.只用一个连接,而另一个在select 子句中用子查询获得:
select .....,(select xx from c where id=a.id) as xx
from .... a left join ... b on a.id=b.id