Oracle触发器写法和举例[通俗易懂]

CREATE OR REPLACE TRIGGER "TR_NUTRITION"
 after update on inp_bill_detail
  for each row
declare
    myexp exception;
    execDate date;
    recordId varchar2(30);
begin
    recordId :=:new.exec_record_id;
    if :new.exec_record_id is not null then
        select nvl(oen.verify_date,oer.execute_date_time) into execDate
        from orders_executed_record oer left join orders_executed_nutrition oen on oer.record_id=oen.record_id
        where oer.record_id = recordId ;
        if execDate is not null then
           raise myexp;
         end if;
    end if;
    exception
        when myexp then raise_application_error('-20002', '计费后,执行(核对)日期不能为空,计费ID=' || :new.detail_no || ' 执行ID=' || recordId);
end ;