随机选取sum(列)=5的记录
表   a
Id         Count
1           2
2           2
3           1
4           1
5           2
6           2
7           1
8           2
9           1
10         2

我想从上表中随机选取几条记录，这几条记录的sum(Count)   =   5

sql应如何写？
多谢！！

------解决方案--------------------
drop table a
CREATE TABLE a (Id int, Count int)
insert a
select 1 , 2
union all select 2 , 2
union all select 3 , 1
union all select 4 , 1
union all select 5 , 2
union all select 6 , 2
union all select 7 , 1
union all select 8 , 2
union all select 9 , 1
union all select 10 , 2

declare @tb table(num varchar(50),id int,Count int)
insert @tb
select newid(),* from a

select * from @tb c where 5> =(select sum(count) from @tb t where c.num> =t.num)