触发器

create sequence seqrole start with 4

create or replace trigger truserrolsinsert
before insert
on userroles
for each row
begin
if inserting then
select seqrole.nextval into :new.id from dual;（

将序列seqrole的下一个值 赋给新插入数据的id

）
end if;
end;

insert into userroles values(0,'xx')

select * from userroles

2，

create or replace trigger truserrolsupdateordelete
after delete or update
on userroles
for each row
begin
if :old.id=3 then
dbms_output.put_line('管理员不能改也不能删除');
rollback;
end if;
end;

delete from userroles where id>=4
update userroles set name=name;

3，instead of 执行删除更新操作时触发，代替delete or update on viewUsers

for each row

create view viewUsers2
as
select * from users;

select * from viewUsers2
delete from viewUsers where id=3

create or replace trigger trviewUsersupdateordelete
instead of delete or update
on viewUsers
for each row
begin
dbms_output.put_line('要删除的用户是:'||:old.name);
end;

delete from viewUsers

select * from viewUsers