Example of trigger:

There are three tables: studinfo, result and update_studinfo. If you insert data into studinfo then that data will be inserted into result with calculation automatically. If you update any data then new data will be inserted into result and old data will be inserted into update_studinfo. If you delete any data then old data will be inserted into update_studinfo table.

You can do that in following way:

create table studinfo
(studid varchar2(3),
name varchar2(15),
php number(3),
oracle number(3),
vb number(3));


create table result
(studid varchar2(3),
name varchar2(15),
php number(3),
oracle number(3),
vb number(3),
total number(3),
per number(6,2),
operation varchar2(7),
op_date date);


create table update_studinfo
(studid varchar2(3),
name varchar2(15),
php number(3),
oracle number(3),
vb number(3),
operation varchar2(7),
op_date date);


create or replace trigger trgstudinfo
before insert or update or delete
on studinfo
for each row
declare
total number;
per number(6,2);
begin
  if inserting then
    total:=:new.php+:new.oracle+:new.vb;
    per:=total/3;
    insert into result values(:new.studid,:new.name,:new.php,:new.oracle,:new.vb,total,per,'INSERT',sysdate);
  end if;

  if updating then
    total:=:new.php+:new.oracle+:new.vb;
    per:=total/3;
    insert into result values(:new.studid,:new.name,:new.php,:new.oracle,:new.vb,total,per,'UPDATE',sysdate);
    insert into update_studinfo values(:old.studid,:old.name,:old.php,:old.oracle,:old.vb,'UPDATE',sysdate);
  end if;

  if deleting then
     insert into update_studinfo values(:old.studid,:old.name,:old.php,:old.oracle,:old.vb,'DELETE',sysdate);   
  end if;

end;
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