SQL> select * from employees;

A
----------
HAI_

SQL> insert into employees values('OK?');

1 row created.

SQL> insert into employees values('OK+?');

1 row created.

SQL> commit;

Commit complete.
SQL> CREATE OR REPLACE PROCEDURE replace1 IS
BEGIN
FOR tm IN (select a from employees) LOOP
UPDATE Employees
SET a = Replace(a, '+', '_');
Update employees
SET a = Replace(a, '?', '_');
END LOOP;
end;  2    3    4    5    6    7    8    9
 10  /

Procedure created.

SQL> exec replace1;

PL/SQL procedure successfully completed.

SQL> select * from employees;

A
----------
HAI_
OK_
OK__

CREATE OR REPLACE PROCEDURE replace1 IS

	cursor c1 is
		(select '?' replace_char from dual
		union
		select '+' replace_char from dual
		union
		select '%' replace_char from dual);
BEGIN
FOR tm in c1 LOOP
UPDATE Employees
SET owner_name = Replace(owner_name, tm.replace_char, '_');
END LOOP;
end;