如何组织SQL语句？

[huyidehyd]

create table a(a decimal(18,2),c varchar(10))
select * from a
insert into a values(5.5,1)
insert into a values(4.5,1)

create table b(a decimal(18,2),b int(4),c varchar(10))
select * from b
insert into b values(2.5,2,1)
insert into b values(5,1,1)

我用的sql语句是：

SELECT sum(a.a) as Sum1,sum(b.a*b.b) as Sum2
FROM a,b
WHERE a.c = '1' AND a.c=b.c
得到：
sum1=20，sum2=20

我想取a.c=b.c=1是的sum1,sum2

[txlicenhe]

create table a(a decimal(18,2),c varchar(10))
--select * from a
insert into a values(5.5,1)
insert into a values(4.5,1)

create table b(a decimal(18,2),b int,c varchar(10))
--select * from b
insert into b values(2.5,2,1)
insert into b values(5,1,1)

SELECT sum(a.a) as Sum1,sum(b.a*b.b) as Sum2
FROM a join b on a.c = b.c
WHERE a.c = '1'

Sum1 Sum2
---------------------------------------- ----------------------------------------
20.00 20.00

（所影响的行数为 1 行）

[yujohny]

create table a(a decimal(18,2),c varchar(10))
--select * from a
insert into a values(5.5,1)
insert into a values(4.5,1)

create table b(a decimal(18,2),b int,c varchar(10))
--select * from b
insert into b values(2.5,2,1)
insert into b values(5,1,1)

SELECT (select sum(a) from a where c=1) as Sum1,(select sum(a*b) as Sum2 from b where c=1) as Sum1


drop table a
drop table b

[huyidehyd]

和我的结果一样啊，可能没说清楚，20不是我想要的结果！

我想取得是当a.c=1 and b.c=1时，
a表a列的和，为10；b表a*b后的和，为10