ORACLE avg,max,min salary TRIGGER - oracle

Question

so i'm trying to create a trigger, but always have an error that says
Trigger LOG_SALARY compiled
LINE/COL ERROR
--------- ------------------------------------------------------------- 2/2 PL/SQL: SQL Statement ignored 3/9 PL/SQL: ORA-00934: group
function is not allowed here Errors: check compiler log
Error(2,2):PL/SQL: SQL Statement ignored
Error(3,9):PL/SQL:ORA-00934:group function is not allowed here
this is my code
'''alter table department add AVG_SALARY number(10);
alter table department add MAX_SALARY number(10);
alter table department add MIN_SALARY number(10);
insert into department (AVG_SALARY, MAX_SALARY, MIN_SALARY) values (AVG(salary), MAX(salary) ,MIN(salary));
create or replace TRIGGER log_salary
after update of salary on employee
for each row
begin
insert into DEPARTMENT(AVG_SALARY, MAX_SALARY, MIN_SALARY)
values(AVG(SALARY),MAX(SALARY),MIN(SALARY));
end;
update department
set salary = salary + 100.0
where SSN =888665555;
select * from DEPARTMENT;'''
could you tell me what is wrong with my code?
thankyou in advance!

Answer 1

You are inserting new rows into the department table. I think you want to update them. The logic looks like this:
create or replace TRIGGER log_salary
after update of salary on employee
for each row
begin
update department
set (AVG_SALARY, MAX_SALARY, MIN_SALARY) =
(select AVG(SALARY), MAX(SALARY), MIN(SALARY)
from employee
where e.department_id = :new.department_id
end;
This however will probably generate a mutating table error. Addressing that is really difficult. For instance, consider this:
emp_id dept_id salary
1 1 10
2 1 10
3 1 5
If you change emp_id's salary to 20, then the max is 20. But if you change the salary to 5, then the max remains 10.
I would suggest that you just use a view to calculate the values on-the-fly.