DML觸發器學習
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??? 來了解一下觸發器的建立方法，以及各類觸發器的簡單介紹。首先看DML觸發器的語法：
??? CREATE [OR REPLACE] TRIGGER trigger_name
??? {BEFORE | AFTER }
??? {INSERT | DELETE | UPDATE [OF column [, column ...]]}
??? ON {[schema.] table_name | [schema.] view_name}
??? [PRFERENCING {OLD [AS] old | NEW [AS] new | PARENT as parent}]
??? [FOR EACH ROW ]
??? [WHEN condition]
??? Trigger body;
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??? 說明：
??? 1、BEFORE/AFTER：指觸發時間在DML操作之前還是之后(對表配置約束時特別有用)
??? 2、DML包括INSERT、DELETE、UPDATE(可以只針對某幾列)
??? 3、FOR EACH ROW：表明是行級觸發器
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DML觸發器示例
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??? 1、創建信息表和最終表
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??? create table t11(a int,b varchar2(100));
??? insert into t11 values(1,'aaa');
??? insert into t11 values(1,'bbb');
??? insert into t11 values(1,'ccc');
??? insert into t11 values(2,'ddd');
??? insert into t11 values(2,'eee');
??? insert into t11 values(3,'fff');
??? insert into t11 values(4,'ggg');
??? insert into t11 values(5,'hhh');
??? commit;
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??? create table t1_log(
?????? who varchar2(30),
?????? poer_date date
?????? );
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??? 2、創建觸發器
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??? create or replace trigger delete_trigger
????? after delete
????? on t11
????? for each row --行級觸發器
??? begin
????? insert into t1_log values(user,sysdate);
??? end;
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??? 3、測試
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??? delete from t11 where a=1;
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??? SQL> select * from t1_log;
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??? WHO????? POER_DATE
??? ------- -------------------
??? WXQ????? 2008-11-2 14:04:38
??? WXQ????? 2008-11-2 14:04:38
??? WXQ????? 2008-11-2 14:04:38
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??? 注：若沒有for each row語句，則只插入一行記錄。
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觸發器的級聯
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??? create table t1_a(id int);
??? create table t1_b(id int);
??? create table t1_c(id int);
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??? create trigger tr_a
????? after insert
????? on t1_a
??? begin
????? insert into t1_b values(1);
??? end; --插入t1_a時，插入t1_b
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??? create trigger tr_b
????? after insert
????? on t1_b
??? begin
????? insert into t1_c values(1);
??? end; --插入t1_b時，插入t1_c
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??? create trigger tr_c
????? after insert
????? on t1_c
??? begin
????? update tr_a set tr_a.id=tr_a.id+10;
??? end; --插入t1_c時，更新t1_a
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??? 測試：
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??? SQL> insert into t1_a values(5);
??? 1 row inserted
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??? SQL> select * from t1_a;
?????? ID
??? -----
?????? 15
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多條件觸發器
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??? CREATE OR REPLACE TRIGGER
??? BEFORE INSERT OR UPDATE OR DELETE
??? BEGIN
????? IF inserting THEN
????? --insert語句觸發
????? ELSIF updating THEN
????? --update語句觸發
????? ELSIF deleting THEN
????? --delete語句觸發
????? END IF;
??? END;
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??? 注：若要針對update某一列，則用 IF UPDATING('xx') THEN...
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??? 具體舉例：
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??? create or replace trigger oper_trigger
????? before insert or update or delete
????? on t1
??? declare
????? str_action varchar2(100);
??? begin
????? if inserting then
??????? str_action:='Insert';
????? end if;
????? if updating then
??????? str_action:='Update';
????? end if;
????? if deleting then
??????? str_action:='Delete';
????? end if;
????? insert into t1_log values(str_action,sysdate);
??? end;
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行級觸發器特性
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1、簡單舉例
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??? create or replace trigger reco_trigger
????? after delete
????? on t11
????? for each row
??? begin
????? insert into t22 values(:old.a,:old.b);
??? end;
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2、說明：
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??? * 可以通過:new和:old來獲得操作前后的不同數據映像
??? * update可同時使用:new、:old，insert只能用:new，delete只能用:old
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3、通過REFERENCING修改映像標識符
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??? create or replace trigger reco_trigger
????? before update
????? on t11
????? referencing new as my_value --注意格式
????? for each row
????? when (my_value.a > 10) --新值大于10時才觸發
??? begin
????? insert into t22 values(:my_value.a,:my_value.b);
??? end;
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??? 注意：即使重命名了，但是還是要在前面加“:”，但是在referencing和when字句中不用加
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