Oracle触发器Trigger4触发条件_when的使用

/*
同一表使用所有条件
Create or replace trigger t5 
      Before  insert,delete,update  on 表名
     For each row
    //plsql块

*/
/*
在触发器中，还有三个变量：都是boolean
    INSERTING 正在执行insert吗。
    DELETING
    UPDATING

*/
select TABLE_NAME from USER_TABLES;
select * from trigger_t2;
desc trigger_t2;
create or replace trigger t4
before INSERT OR UPDATE or delete on trigger_t2
  FOR EACH ROW
  declare
  begin
  if inserting then
  dbms_output.put_line(‘写入‘);
  elsif deleting then
  dbms_output.put_line(‘删除‘);
  else 
  dbms_output.put_line(‘更新‘);
end if;
end;
---测试
set serveroutput on;
insert into trigger_t2 values(1,‘jk‘,23);
delete from trigger_t2 where id=1;
update trigger_t2 set name=‘kk‘;
---------------------------------------------------
---------------------------------------------------
--使用when语句设置条件
create or replace trigger t5
before INSERT on trigger_t2
  FOR EACH ROW
  when (NEW.age<=18)
  declare
  begin
  DBMS_OUTPUT.PUT_LINE(‘大于20是：‘||:NEW.age);
  RAISE_APPLICATION_ERROR(-20000, ‘年龄小于18不能参与‘);
end;
set serveroutput on;
INSERT INTO TRIGGER_T2 VALUES(4,‘KK‘,22);
/*
--禁用trigger
alter trigger t4 disable;
alter trigger t4 enable;
--修改名称
alter trigger t4 rename to t5;
*/