oracle觸發器，triggers

:new --爲一個引用最新的列值;
:old --爲一個引用之前的列值; 這兩個變量只有在使用了關鍵字 "FOR EACH ROW"時才存在.且update語句兩個都有,而insert只有:new ,delect 只有:old;

系統中的觸發器實例：

create or replace trigger JBPM.TIB_DEPLOYBYMOVEPAPER before //before表示在操做完成前觸發，                                                                                                             after表示在完成後觸發

insert //發生插入數據操做觸發
on JBPM.DEPLOYBYMOVEPAPER for each row //指定觸發器每行觸發一次
declare
    integrity_error exception; //用戶自定義錯誤
    errno            integer;
    errmsg           char(200);
    dummy            integer;
    found            boolean;
    row_count number;
    max_num deploybymovepaper.num%type; //根據表的字段定義變量類型
    zero_today deploybymovepaper.num%type;

begin
-- Column "ID" uses sequence SEQUENCE_38
case
when inserting then //SQL語句只能使用:new特殊變量
select SEQUENCE_38.NEXTVAL INTO :new.ID from dual;//主鍵自增
zero_today :='0391'||to_char(sysdate,'yymmdd')||lpad(to_char(0),4,'0');//lpad函數定義字符串長度                                                                                                               爲4不足時用0補全
    select count(*) into row_count from deploybymovepaper;
    if row_count = 0 then
        max_num:=zero_today;//:=給變量賦值
    else
      select max(num) into max_num from deploybymovepaper;
    end if;
    if max_num<zero_today then
        max_num:=zero_today;
    end if;
    if :new.num is null then
    :new.num:=lpad(to_char(to_number(max_num)+1),14,'0'); //遞增編號，有14爲數字組成
    end if;
when updating('num') then//:new、:old均可以用
if :new.num!=:old.num then
      :new.num:=:old.num;
end if;
end case;

-- Errors handling
exception
    when integrity_error then
       raise_application_error(errno, errmsg); //拋出異常語句
end;