求对数值范围判定SQL语句？

[asdw001]

表a的结构如下：
id  t   a1
1   ta  0   
2   tc  4           
3   tt  7   
4   rt  7   
5   gg  14   
6   sr  22   
7   qq  4   
8   sd  7   
9   vs  50   
10  ws  10   
11  rf  9   

要求对表a中a1列的数值进行判定，结果输到b表中。
若值在0---5之间，对应的b1列上标明b05
若值在6---9之间，对应的b1列上标明b69
若值在10---14之间，对应的b1列上标明small
若值在15---30之间，对应的b1列上标明big
若值在30之上，对应的b1列上标明null

判定后，b表的结果如下：
id  t   a1   b1
1   ta  0    b05
2   tc  4    b05       
3   tt  7    b69
4   rt  7    b69
5   gg  14   small
6   sr  22   big
7   qq  4    b05
8   sd  7    b69
9   vs  50   null
10  ws  10   small
11  rf  9    b69

/*表a的代码如下：
create table a(id int,t text,a1 int) 
insert into  a  values(1,'ta',0) 
insert into  a  values(2,'tc',4)         
insert into  a  values(3,'tt',7) 
insert into  a  values(4,'rt',7) 
insert into  a  values(5,'gg',14) 
insert into  a  values(6,'sr',22) 
insert into  a  values(7,'qq',4) 
insert into  a  values(8,'sd',7) 
insert into  a  values(9,'vs',50) 
insert into  a  values(10,'ws',10) 
insert into  a  values(11,'rf',9) 
go*/

[bqb]

select id,t,a1,case when a1 between 0 and 5 then 'b05',
                    when a1 between 6 and 9 then 'b09',
                    when a1 between 10 and 14 then 'small',
                    when a1 between 15 and 30 then 'big',
               else null end as b1 from b 

[-狙击手-]

create table a(id int,t text,a1 int) 
insert into  a  values(1,'ta',0) 
insert into  a  values(2,'tc',4)         
insert into  a  values(3,'tt',7) 
insert into  a  values(4,'rt',7) 
insert into  a  values(5,'gg',14) 
insert into  a  values(6,'sr',22) 
insert into  a  values(7,'qq',4) 
insert into  a  values(8,'sd',7) 
insert into  a  values(9,'vs',50) 
insert into  a  values(10,'ws',10) 
insert into  a  values(11,'rf',9) 
go


select id,cast(t as varchar) t,a1,
[b1] =case when a1 between 0  and 5 then 'b05'
           when a1 between 6  and 9 then 'b69'
           when a1 between 10 and 14 then 'small'
           when a1 between 15 and 30 then 'big'
           else 'unknow' end
from a

drop table a

/*

id          t                              a1          b1     
----------- ------------------------------ ----------- ------ 
1           ta                             0           b05
2           tc                             4           b05
3           tt                             7           b69
4           rt                             7           b69
5           gg                             14          small
6           sr                             22          big
7           qq                             4           b05
8           sd                             7           b69
9           vs                             50          unknow
10          ws                             10          small
11          rf                             9           b69

（所影响的行数为 11 行）


*/

[-狙击手-]

create table a(id int,t text,a1 int) 
insert into  a  values(1,'ta',0) 
insert into  a  values(2,'tc',4)         
insert into  a  values(3,'tt',7) 
insert into  a  values(4,'rt',7) 
insert into  a  values(5,'gg',14) 
insert into  a  values(6,'sr',22) 
insert into  a  values(7,'qq',4) 
insert into  a  values(8,'sd',7) 
insert into  a  values(9,'vs',50) 
insert into  a  values(10,'ws',10) 
insert into  a  values(11,'rf',9) 
go


select id,cast(t as varchar) t,a1,
[b1] =case when a1 between 0  and 5 then 'b05'
           when a1 between 6  and 9 then 'b69'
           when a1 between 10 and 14 then 'small'
           when a1 between 15 and 30 then 'big'
           else null end
from a

drop table a

/*

id          t                              a1          b1     
----------- ------------------------------ ----------- ------ 
1           ta                             0           b05
2           tc                             4           b05
3           tt                             7           b69
4           rt                             7           b69
5           gg                             14          small
6           sr                             22          big
7           qq                             4           b05
8           sd                             7           b69
9           vs                             50          NULL
10          ws                             10          small
11          rf                             9           b69

（所影响的行数为 11 行）


*/

[fa_ge]

case when

[桃花岛黄岛主]

都解答出来了,我就接分吧

[bqb]

更正：

 select id,t,a1,case when a1 between 0 and 5 then 'b05'
                    when a1 between 6 and 9 then 'b09'
                    when a1 between 10 and 14 then 'small'
                    when a1 between 15 and 30 then 'big'
               else null end as b1 from a

[areswang]

接了吧，我就不写了。