pb中sql语句用to_char查询出来数据，居然无法检索出数据，oracle数据库，这是什么原因?

 /*这样dw_modified总是无法检索出正确的结果*/
 select nvl(max(to_char(SBLJL01,'')),'')
   into :is_recoder_old_sn
   from emra03
  where szybh01 = :as_pat_id
    and Swdfl01 = :as_emr_code;    

 Integer li_ret
 li_ret = dw_modified.retrieve(as_pat_id,as_emr_code,is_recoder_old_sn)

 /*这样就没事，能得出结果*/
 select max(SBLJL01)
 into :is_recoder_old_sn
 from emra03
 where szybh01 = :as_pat_id
 and Swdfl01 = :as_emr_code;    

 Integer li_ret
 li_ret = dw_modified.retrieve(as_pat_id,as_emr_code,is_recoder_old_sn)

 /*这样也没问题*/
 Long ll_recoder_old_sn
 select max(to_number(SBLJL01))
   into :ll_recoder_old_sn
   from emra03
  where szybh01 = :as_pat_id
    and Swdfl01 = :as_emr_code;

 is_recoder_old_sn = String(ll_recoder_old_sn,"000")

 Integer li_ret
 li_ret = dw_modified.retrieve(as_pat_id,as_emr_code,is_recoder_old_sn)

可是两个select 语句的结果都是023,奇怪不？