Compilation error on oracle trigger - sql

Question

I have a table that has employees (oracle SQL), where each employee has a manager (which is represented as a fk of another employee). I want to create a trigger that when an employee is deleted, all employees that have his key in their manager field have their manager changed to null (or -1, or some reserved value). I'm having some trouble figuring out what's wrong with my current code:
EDIT:
I fixed up most of my code, and I was going about it the wrong way. I used the ON DELETE option that was suggested and now everything works fine. Here's my code:
CREATE TABLE EmployeeA
(
employeeID integer,
firstName varchar (255),
lastName varchar (255),
phone integer,
jobTitle varchar (255),
payGrade integer,
fk_EmployeeemployeeID integer,
PRIMARY KEY(employeeID),
FOREIGN KEY(fk_EmployeeemployeeID) REFERENCES EmployeeA (employeeID) ON DELETE SET NULL
);
INSERT INTO EMPLOYEEA VALUES (1, null, 'Powell', 0, 'President', 100, 1);
INSERT INTO EMPLOYEEA VALUES (2, null, 'Hicke', 0, 'Dean (Natural Science)', 100, 1);
INSERT INTO EMPLOYEEA VALUES (3, null, 'Fenves', 0, 'Dean (Engineering)', 100, 1);
INSERT INTO EMPLOYEEA VALUES (4, null, 'Porter', 0, 'Chairman (Computer Science)', 100, 2);
INSERT INTO EMPLOYEEA VALUES (5, null, 'Beckner', 0, 'Chairman (Mathematics)', 100, 2);
INSERT INTO EMPLOYEEA VALUES (6, null, 'Miranker', 0, 'Professor (Computer Science)', 100, 4);
INSERT INTO EMPLOYEEA VALUES (7, null, 'Mok', 0, 'Professor (Computer Science)', 100, 4);
DELETE FROM employeeA WHERE lastName = 'Porter'; 

Answer 1

You don't want to use a trigger here. Use the on delete property of the foreign key. When you define the foreign key constraint, you can specify that you want it to set the child rows to NULL when the parent row is deleted.
SQL> ed
Wrote file afiedt.buf
1 create table employee2(
2 employee_id number primary key,
3 manager_id number,
4 employee_first_name varchar(30),
5 constraint fk_manager_emp
6 foreign key( manager_id )
7 references employee2( employee_id )
8 on delete set null
9* )
SQL> /
Table created.
If we add a boss, a manager (who reports to the boss), and an employee (who reports to the manager)
SQL> insert into employee2( employee_id, manager_id, employee_first_name )
2 values( 1, null, 'Boss' );
1 row created.
SQL> ed
Wrote file afiedt.buf
1 insert into employee2( employee_id, manager_id, employee_first_name )
2* values( 2, 1, 'Emp1' )
SQL> /
1 row created.
SQL> ed
Wrote file afiedt.buf
1 insert into employee2( employee_id, manager_id, employee_first_name )
2* values( 3, 2, 'Emp2' )
SQL> /
1 row created.
then when we delete the manager, the employee's manager_id automatically gets set to NULL
SQL> delete from employee2
2 where employee_first_name = 'Emp1';
1 row deleted.
SQL> select *
2 from employee2
3 where employee_first_name = 'Emp2';
EMPLOYEE_ID MANAGER_ID EMPLOYEE_FIRST_NAME
----------- ---------- ------------------------------
3 Emp2