关于Case when 的问题

[lostvivi]

select distinct b.location from imp_bb_mod a,ch_bb b, ch_ll c 
where DECODE(a.old_ll_number,NULL, a.ll_number,a.old_ll_number) = c.l_number 

上面是Oracle中的查询语句，下面是在SQLServer中的查询语句

select distinct b.location 
from imp_bb_mod a,ch_bb b, ch_ll c 
where 
c.l_number= case a.old_l_number when null then a.l_number else a.old_l_number end 

SQLServer中的是我写的，不知道是哪里用错了，有数据却查不出来数据，请大家帮忙看看

[dobear_0922]

select distinct b.location 
from imp_bb_mod a,ch_bb b, ch_ll c 
where 
c.l_number=isnull(a.old_l_number,a.l_number)

[dobear_0922]

--or
select distinct b.location 
from imp_bb_mod a,ch_bb b, ch_ll c 
where 
c.l_number= case when a.old_l_number is null then a.l_number else a.old_l_number end 

[fa_ge]

楼上正解

[pt1314917]

那个高手已经把答案都贴出来了。。。。。。