Triggers in PL-SQL - sql

Question

I have two tables:
create table speciality(
major varchar2(30),
total_credits number,
total_students number);
create table students(
id number(5) primary key,
first_name varchar2(20),
last_name varchar2(20),
major varchar2(30),
current_credits number(3));
I want to create a trigger that carries the name UpdateSpeciality that deletes, updates and inserts into speciality table right when the same operation happens on students table.
This is how the speciality table should look after the following:
SQL> INSERT INTO STUDENTS(id, first_name, last_name, major, current_credits) values(10001, 'sam', 'ali', 'computer science', 11);
SQL>INSERT INTO STUDENTS(id, first_name, last_name, major, current_credits) values(10002, 'kevin', 'mark', 'MIS', 4);
SQL>INSERT INTO STUDENTS(id, first_name, last_name, major, current_credits) values(10003, 'robert', 'jack', 'computer science', 8);
How can I solve this? I don't know how to connect the two tables.
Should I use stored procedures?
CREATE OR REPLACE TRIGGER UpdateSpeciality
after insert or delete or update on students
for each row
begin
if inserting /* this is how far i got */

Answer 1

Something like this should do it. With some assumtions :)
CREATE OR REPLACE TRIGGER UpdateSpeciality
after insert or delete or update on students
for each row
declare
cursor c_spec(sMajor speciality.major%type) is
select * from speciality
where major = sMajor
for update;
r_spec c_spec%ROWTYPE;
begin
if inserting then
open c_spec(:new.major);
fetch c_spec into r_spec;
if c_spec%FOUND then
update speciality set
total_credits = total_credits + :new.current_credits,
total_students = total_students + 1
where current of c_spec;
else
insert into speciality(major, total_credits, total_students) values (:new.major, :new.current_credits, 1);
end if;
close c_spec;
elsif updating then
open c_spec(:new.major);
fetch c_spec into r_spec;
if c_spec%FOUND then
update speciality set
total_credits = total_credits + :new.current_credits - :old.current_credits
where current of c_spec;
else
insert into speciality(major, total_credits, total_students) values (:new.major, :new.current_credits, 1);
end if;
close c_spec;
elsif deleting then
open c_spec(:old.major);
fetch c_spec into r_spec;
if c_spec%FOUND then
update speciality set
total_credits = total_credits - :old.current_credits ,
total_students = total_students - 1
where current of c_spec;
if r_spec.total_students = 1 then
delete from speciality where major = :old.major;
end if;
end if;
close c_spec;
end if;
end;