Bind variable error in triggers Oracle PL/SQL - oracle

Question

mgr table is the table with employeessn, mgrssn, and salary. It takes data from employee table and department table.
create table mgr as
select ssn, mgrssn, salary
from Employee E
join Department D
on E.Dno = D.Dno;
select * from mgr;
Here is my trigger
create or replace trigger check_sal
for insert or update on employee
compound trigger
type t_ch_tab is table of mgr%rowtype;
g_ch_tab t_ch_tab := t_ch_tab();
after each row is
begin
g_ch_tab.extend;
g_ch_tab(g_ch_tab.last).ssn := :new.ssn;
g_ch_tab(g_ch_tab.last).mgrssn := :new.mgrssn;
g_ch_tab(g_ch_tab.last).salary := :new.salary;
end after each row;
after statement is
l_sal employee.sal%type;
begin
for i in g_ch_tab.first .. g_ch_tab.last loop
select e.salary
into l_salary
from employee e
where e.ssn = g_ch_tab(i).mgrssn;
if g_ch_tab(i).salary > l_salary then
raise_application_error(-20001, 'Employee''s salary can not be higher than manager''s salary');
end if;
end loop;
end after statement;
end check_sal;
I am getting the following error.
Error(17,45): PLS-00049: bad bind variable 'NEW.MGRSSN'

Answer 1

create table department (
mgrssn varchar2(100),
dno number);
create table employee (
ssn varchar2(100),
salary number,
dno number
);
create table mgr as select ssn,mgrssn,salary,e.dno from Employee E, Department D where E.Dno = D.Dno;
create or replace trigger check_sal
for insert or update on employee
compound trigger
type t_ch_tab is table of mgr%rowtype;
g_ch_tab t_ch_tab := t_ch_tab();
after each row is
begin
g_ch_tab.extend;
g_ch_tab(g_ch_tab.last).ssn := :new.ssn;
-- g_ch_tab(g_ch_tab.last).mgrssn := :new.mgrssn;
g_ch_tab(g_ch_tab.last).salary := :new.salary;
g_ch_tab(g_ch_tab.last).dno := :new.dno;
end after each row;
after statement is
l_salary employee.salary%type;
begin
for i in g_ch_tab.first .. g_ch_tab.last loop
select e.salary
into l_salary
from employee e, department d
-- where e.ssn = g_ch_tab(i).mgrssn;
where e.ssn = d.mgrssn
and e.dno = g_ch_tab(i).dno;
if g_ch_tab(i).salary > l_salary then
raise_application_error(-20001, 'Employee''s salary can not be higher than manager''s salary');
end if;
end loop;
end after statement;
end check_sal;