select  (case when  a.TOTALNETUNIT is not null then 
  (  select c.TOTALNETUNIT  from FND_DERNAV c  where  c.SECUCODE=a.secucode and rownum=1 order by c.enddate desc      )
 else a.totalnetunit 
  end) as MyColumn  
  from FND_DERNAV a inner join FND_DAILYQUOTE b on a.SECUCODE=b.secucode and b.TRADINGDAY=a.ENDDATE

 and rownum=1 order by c.enddate desc

------解决方案--------------------
探讨


引用:

不说语法问题，单看你这个SQL code
and rownum=1 order by c.enddate desc
的用法就有问题，rownum是个伪列，是先于order by子句执行的，所以你加个按结束日期排序毫无意义，不信你把desc改成asc看看，结果是一样的。

select* from FND_DERNAV  where  rownum=1  o……