创建触发器

create or replace trigger tr_test
  before insert or update or delete on log_student 

declare
 content varchar(20);
begin
 if inserting then
content :='新增';
elsif updating then
content:='修改';
else
content:='删除';
end if;
insert into log_student values(seq.nextval,content,sysdate);
end tr_test;

限制操作（只能在星期一或星期五修改）；

create or replace trigger tr_command
  before insert or update or delete on student 
declare
begin
  if(TO_CHAR(SYSDATE,'DY') not IN ('MON','FRI')) then
    RAISE_APPLICATION_ERROR(-20500,'非法时间修改表错误');
  end if;
end tr_command;