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oracle 笔记 V 之触发器 (TRIGGER)

 触发器 trigger
分类:前触发,后触发
      行触发器,语句触发器
行触发器与语句触发器的区别:
行触发器要求当一个 DML 语句操作影响数据库中的多行数据时,对于其中的每个数据行,只要它们符合触发约束条件,均激活一次触发器,FOR EACH ROW 选项说明触发器为行触发器;
语句触发器将整个语句操作 作为触发事件,当它们符合约束条件时,激活一次触发器
创建语法:
create or replace trigger trigger_name
       before |after
       insert |delete | update |{[of column[,column ...]]
       on [schema.]table_name
 for each row
       [when condition]
 trigger_body;
eg(仔细体会):
create or replace trigger hello_tri
        before insert or delete or update on emp
        for each row
begin
       dbms_output.put_line('我是触发器!');
end;


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