表A
id name amount
---------------------------
1 xxx 1000.00
2 yyy 500.00
tableB的
idkey project alloted
--------------------------------------
1 xxx 500.00
1 xxx 500.00
2 yyy1 250.00
2 yyy2 250.00
表C
idkey Proj item cost
-----------------------------
1 xxx hammer 500.00
1 xxx nail 200.00
1 xxx labor 200.00
2 yyy1 chair 150.00
2 yyy1 table 100.00
2 yyy2 chain 100.00
2 yyy2 spring 50.00
，输出就像这样
idkey name tot_allo tot_cost
1 xxx 1000.00 900.00
2 yyy 500.00 400.00
以及我已经拥有的......
SELECT tableA.name, SUM(tableB.alloted) as tot_allo,
SUM(tableC.cost) as tot_cost
FROM tableA LEFT JOIN tableB ON tableA.idkey = tableB.idkey
LEFT JOIN tableC ON tableB.idkey = tableC.idkey
GROUP BY tableA.name
并且这个输出不是我所期待的... tot_allo和tot_cost它使自己的数量加倍......为什么？
table.A.name, tot_allo, tot_cost
--------------------------------------
xxx 2000.00 1800.00
yyy 1000.00 400.00
我会很高兴有任何帮助:)
答案 0 :(得分：1)
在加入之前，您需要使用子查询来获取聚合：
select A.idkey,
A.name,
B.tot_allo,
C.tot_cost
from tableA A
left outer join (
select idkey, sum(alloted) as tot_allo
from tableB
group by idkey
) B on B.idkey = A.idkey
left outer join (
select idkey, sum(cost) as tot_cost
from tableC
group by idkey
) C on C.idkey = A.idkey
使用观点：
create view v_tableB_totals
as
select idkey, sum(alloted) as tot_allo
from tableB
group by idkey
create view v_tableC_totals
as
select idkey, sum(cost) as tot_cost
from tableC
group by idkey
select A.idkey,
A.name,
B.tot_allo,
C.tot_cost
from tableA A
left outer join v_tableB_totals B
on B.idkey = A.idkey
left outer join v_tableC_totals C
on C.idkey = A.idkey