这样一道sql查询面试题，该怎样实现？

[canyangruxie]

今天去面试，有一道题是这样的：
有a,b 两张表：
表a 表b
id dic id com
1 1 12
2 1 23
3 2 4
4 2 42
5 3 4
4 9
4 7
要求:写一条sql语句，把表b按id分组,然后把分组后的sum(com)按id插入相应的表a的dic列.
注意：只能写一条语句!

[ZengHD]

insert a select sum(com) from b group by id

[我姓区不姓区]

insert into a select id,com from (select id,sum(com) as com from b group by id) as t 

[sunxw18]

insert into b select id ,sum(com) from b group by id

[sunxw18]

insert into a select id ,sum(com) from b group by id

[yangpeiyu]

简单啦。
那A的ID如果是不需要我们插就

insert into a(com) 
select com from 
(select id ,sum(com) as com from b group by id) as a

如果那A的ID都要插进去的话就。

insert into a(com) 
select id ,sum(com) as com from b group by id

[chinaicm]

insert into a select id,sum(com) from com group by id

[lijin84100]

insert into b select id ,sum(com) from b group by id

[rohan]

很负责任的说一句，上面的全错！
正确代码

update a set dic=(select sum(com) as dic from b where b.id=a.id group by id)

[mators]

update t2 set t2.sums=c.com
from (select id,sum(com)as com from t1 group by id) as c
where t2.id=c.id

[Smile_Wong1]

update a set dic=(select sum(com) from b group by id having b.id=a.id )

[zouhuiqun]

注意HQL与SQL的区别啊！