求助一个Sql问题...

Question

有如下表  tt
a nvarchar(8)
 b inta            b
--------------------
A           55
A           44
A           4
B           3
B           33
C           43
C           3    
D           4
...         ...
E           54怎样把比D 小的字母的b字段求和啊  
               

Answer 1

select sum(b) from tt where a<'D'

Answer 2

select sum(b) from tt where a<'D'

Answer 3

select sum(B) from tt where ASCII(A)<ASCII('D')

Answer 4

select sum(b) from tt where a<'D'

Answer 5

select sum(b) from tt where a<'D'