如何在Oracle中获得当前的生效日期？

尝试：

select TID,       TName,       EffectiveDate,       depre(sign(EffectiveDate - (select max(T2.EffectiveDate)    from MyTable T2   where T1.Tname=T2.Tname and          T2.EffectiveDate <= sysdate)),   -1,'Invalid',   0,'Valid',   'Inactive') Statusfrom MyTable T1