关于select里加入条件判断的问题!!!!!!!!!!!!!

[苯苯苯熊PK]

SQL如下
select fid,fnumber,case when fbilltype=2 then fnumber else '' end
from a
我要实现的是，当fbilltype=2时取fnumber字段的值否则取空值（fbilltype是数字型字段,fnumber是字符串）。我在执行时提示我类型不匹配，怎么回事？
我该怎么写这个SQL呢？

[liangCK]

select fid,fnumber,case when fbilltype=2 then ltrim(fnumber) else '' end
from a

[Limpire]

 select fid,fnumber,case when fbilltype=2 then ltrim(fnumber) else '' end from a

[Limpire]

select fid,fnumber,case when fbilltype=2 then ltrim(fnumber) else '' end from a

[arrow_gx]

select fid,fnumber,case when fbilltype=2 then cast(fnumber as varchar(100)) else '' end from a

[pt1314917]

select fid,fnumber,case when fbilltype=2 then ltrim(fnumber) else '' end 
 from a 

[忆轩辕]

用case when实现

[dawugui]

[Quote=引用楼主 wcjmecn 的帖子:]
SQL如下
select fid,fnumber,case when fbilltype=2 then fnumber else '' end
from a
我要实现的是，当fbilltype=2时取fnumber字段的值否则取空值（fbilltype是数字型字段,fnumber是字符串）。我在执行时提示我类型不匹配，怎么回事？
我该怎么写这个SQL呢？
[/Quote]

select fid,fnumber,case when fbilltype = 2 then fnumber else null end from a 

select fid,fnumber,case when fbilltype = 2 then cast(fnumber as varchar) else '' end from a