select 
substr(id, 1,length(id)-4) as id
from test;

------解决方案--------------------
select substr(id,length(id)-4+1) as id
from test;

------解决方案--------------------
 select substr(c1,length(c1)-4+1) from t1

------解决方案--------------------

SQL code

SQL> with tmp as (
  2       select '12345' data from dual union all
  3       select '1' data from dual union all
  4       select '123' data from dual
  5       )
  6  select substr(data, -least(length(data), 4))
  7    from tmp;
 
SUBSTR(DATA,-LEAST(LENGTH(DATA
------------------------------
2345
1
123