Use to_number function with order by raise invalid number error

Hi all,

I meet an error when I use to_number function with order by, it happened as follow:

table schema like :

Create table t_ss(

SID int,

S_CLASS varchar2(30)

)

Create table t_sst (

SID int,

TID int,

STT char(4),

NAME varchar2(20)

)

and I also have two view like:

Create view v_ss_t1

AS

select t.SID,t.TID,t.STT,t.NAME SRC,s.NAME DST from t_sst t left join t_sst s on t.TID+1=s.TID;

Create view v_ss_t2

AS

select a.SID,a.S_CLASS,b.TID,b.STT,b.SRC,b.DST from t_ss a,v_ss_t1 b where a.SID=b.SID order by STT;