SQL> create table test1
  2  (NO   VARCHAR2(5),
  3   NAME VARCHAR2(10),
  4   FLG  VARCHAR2(1)
  5  );

Table created.

SQL> create or replace trigger trg_test1
  2    before insert on test1
  3    for each row
  4  begin
  5    :new.name := 'EMP' || :new.name;
  6  end;
  7  /

Trigger created.

SQL> insert into test1 (no, name, flg) values ('A', 'Little', '1');

1 row created.

SQL> select * from test1;

NO    NAME       F
----- ---------- -
A     EMPLittle  1

SQL>