征求sql语句

[nuaawyd]

表A,字段a1,a2
数据如下
a1 a2
11 432
12 43
34 45
...

现在需要类似这样的结果：(11*432+12*43+34*45)/(11+12+34) （a1*a2/sum(a1)）
请问语句怎么写？

[子陌红尘]

select sum(a1*a2)/sum(a1) from 表A

[zanyzyg]

select sum(a1*a2)/sum(a1) from a

[青锋-SS]

select sum(isnull(a1,0)*isnull(a2,0))/sum(isnull(a1,0)) from 表A

[fcuandy]

select sum(a1*a2)/isnull(nullif(sum(a1),0),1) from 表A

[laowan688]

declare @table table
(
a1 int,
a2 int
)
insert @table select 11,432
union select 12,43
union select 34,45
select (sum(a1*a2)/sum(a1)) from @table