Can someone help me to fix an error pls-00049? - oracle

Question

i have created a trigger to my Oracle task and got some errors and i'm trying to solve but don't know how. I was searching fix to my error but i didn't find helpful solution
Is someone can help me to do it, please?
So here's my code:
create table sourcetablename_log (
id number,
operation_date date,
old_username varchar2(20),
new_username varchar2(20),
old_first_name varchar2(20),
new_first_name varchar2(20),
old_last_name varchar2(20),
new_last_name varchar2(20),
action varchar2(20),
author varchar2(20)
);
create or replace trigger src_log
before insert or delete or update on sourcetablename_log
for each row
begin
if inserting then
insert into sourcetablename_log(id, operation_date, new_username, new_firstname, new_lastname)
values (:new.id, sysdate, :new.username, :new.firstname, :new.lastname);
elsif updating then
insert into sourcetablename_log(id, operation_date, old_username, new_username, old_firstname, new_firstname, old_lastname, new_lastname)
values (:new.id, sysdate, :old.username, :new.username, :old.firstname, :new.firstname, :old.lastname, :new.lastname);
elsif deleting then
insert into sourcetablename_log(id, operation_date, old_username, new_username, old_firstname, new_firstname, old_lastname, new_lastname)
values (:new.id, sysdate, :old.username, :new.username, :old.firstname, :new.firstname, :old.lastname, :new.lastname);
end if;
end src_log;
And here's an error:
LINE/COL ERROR
--------- -------------------------------------------------------------
4/27 PLS-00049: bad bind variable 'NEW.USERNAME'
4/42 PLS-00049: bad bind variable 'NEW.FIRSTNAME'
4/58 PLS-00049: bad bind variable 'NEW.LASTNAME'
7/27 PLS-00049: bad bind variable 'OLD.USERNAME'
7/42 PLS-00049: bad bind variable 'NEW.USERNAME'
7/57 PLS-00049: bad bind variable 'OLD.FIRSTNAME'
7/73 PLS-00049: bad bind variable 'NEW.FIRSTNAME'
7/89 PLS-00049: bad bind variable 'OLD.LASTNAME'
7/104 PLS-00049: bad bind variable 'NEW.LASTNAME'
10/27 PLS-00049: bad bind variable 'OLD.USERNAME'
10/42 PLS-00049: bad bind variable 'NEW.USERNAME'
10/57 PLS-00049: bad bind variable 'OLD.FIRSTNAME'
10/73 PLS-00049: bad bind variable 'NEW.FIRSTNAME'
10/89 PLS-00049: bad bind variable 'OLD.LASTNAME'
10/104 PLS-00049: bad bind variable 'NEW.LASTNAME'
Errors: check compiler log
My problem is:
Automate creation of logging table and associated with it triggers A Create a stored procedure that creates a LOGGING table with corresponding columns of OLD values and NEW values, ACTION column, that should be filled in by type of an ACTION and user name (AUTHOR)
Example: You have a table USER of users with next columns:
USERNAME VARCHAR
FIRST_NAME VARCHAR
LAST_NAME VARCHAR
Your procedure should produce a new table with name of “SOURCETABLENAME”_LOG - in this case - USER_LOG with next columns:
ID NUMBER [or OPERATION_ID NUMBER]
OPERATION_DATE DATE
OLD_USERNAME VARCHAR
NEW_USERNAME VARCHAR
OLD_FIRST_NAME VARCHAR
NEW_FIRST_NAME VARCHAR
OLD_LAST_NAME VARCHAR
NEW_LAST_NAME VARCHAR
ACTION VARCHAR
AUTHOR VARCHAR**

Answer 1

If column name is e.g. new_username, then you'd use :new.new_username, not just :new.username.
The same goes for all other columns.
For example:
insert into sourcetablename_log(id, operation_date, new_username, new_firstname, new_lastname)
values (:new.id, sysdate, :new.new_username, :new.new_firstname, :new.new_lastname);