select中嵌套case为何不能用order by

select中嵌套case为何不能用order by

具体代码为：
select bc2.nomb,
        (case when getdate(bc2.putdate,bc2.matdate) ='01'  then
                (select ri.TeamRate
                from rate_info ri
                where ri.rateyear>= replace(bc2.putoutdate,'/','-')
                and ri.teamtime ='1'
                and rownum=1
                order by ri.rateyear asc)       
            else 0  end
          ) businessrate
        from  bc2,
            lc2
          where bc2.nomb = lc2.nomb
          and  bc2.nomb not in(select bd2.no2 from  bd2)
          and bc2.putdate is not null
          and bc2.matdate is not null;

而下面语句确可以正确执行：select ri.TeamRate
                from rate_info ri
                where ri.rateyear>= replace(bc2.putoutdate,'/','-')
                and ri.teamtime ='1'
                and rownum=1
                order by ri.rateyear asc

我子查询的主要目的是查找大于某个日期的最大利率

还有没有什么好的方法可以改进这个子查询，能达到我要求的目标。
 
 

应当是排序之后的最小值。我的case里还有许多其它情况，只是举一个例子。按日期排序，然后取与最小日期对应的利率。

用上GROUP BY 应该 就可以了！
select bc2.nomb,
        (case when getdate(bc2.putdate,bc2.matdate) ='01'  then
                (select ri.TeamRate
                from rate_info ri
                where ri.rateyear>= replace(bc2.putoutdate,'/','-')
                and ri.teamtime ='1'
                and rownum=1
                order by ri.rateyear asc group by ri.rateyear )       
            else 0  end
          ) businessrate
        from  bc2,
            lc2
          where bc2.nomb = lc2.nomb
          and  bc2.nomb not in(select bd2.no2 from  bd2)
          and bc2.putdate is not null
          and bc2.matdate is not null;

select ri.TeamRate
                from rate_info ri
                where ri.rateyear>= replace(bc2.putoutdate,'/','-')
                and ri.teamtime ='1'
                and rownum=1
                order by ri.rateyear asc

此句查询得到的不是最大值吧
select teamrate
from(
select ri.TeamRate
                from rate_info ri
                where ri.rateyear>= replace(bc2.putoutdate,'/','-')
                and ri.teamtime ='1'
                order by ri.rateyear asc
)
where  rownum=1 这样才是对的