select 
  case 
    when type='A' then 
      case 
        when type1=1 then b1
        when type1=2 then b2
      end
    when type='B' then
      case 
        when type1=1 then c1
        when type1=2 then c2
      end
  end
from tb

------解决方案--------------------
SQL code



select *,
       case when type ='A' and tyep1=1 then b1
            when type ='A' and tyep1=2 then b2
            when type ='B' and tyep1=1 then c1
            when type ='B' and tyep1=2 then c2
       end 

from [表]

------解决方案--------------------
SQL code
create table test([id] int,[type] varchar(10),[type1] varchar(10),[b1] varchar(10),[b2] varchar(10),[c1] varchar(10),[c2] varchar(10))
go
insert test
select 1,'A','1','a','a','a','a' union all
select 2,'B','2','b','a','c','d' union all
select 3,'A','2','c','e','a','d' union all
select 4,'B','1','g','a','a','e'

select * from test

declare @type varchar(10),@type1 varchar(10)
set @type='B'
set @type1='1'

declare @sql varchar(max)

select @sql=isnull(@sql,'')+' (case when [type]=''A'' and [type1]=''1'' then b1
 when [type]=''A'' and [type1]=''2'' then b2
 when [type]=''B'' and [type1]=''1'' then c1
 when [type]=''B'' and [type1]=''2'' then b2 end) as val'


print @sql
exec('select id,[type],[type1],'+@sql+' from test order by [type],[type1]' )

drop table test

(4 row(s) affected)
id          type       type1      b1         b2         c1         c2
----------- ---------- ---------- ---------- ---------- ---------- ----------
1           A          1          a          a          a          a
2           B          2          b          a          c          d
3           A          2          c          e          a          d
4           B          1          g          a          a          e

(4 row(s) affected)

 (case when [type]='A' and [type1]='1' then b1
 when [type]='A' and [type1]='2' then b2
 when [type]='B' and [type1]='1' then c1
 when [type]='B' and [type1]='2' then b2 end) as val
id          type       type1      val
----------- ---------- ---------- ----------
1           A          1          a
3           A          2          e
4           B          1          a
2           B          2          a

(4 row(s) affected)