CREATE OR REPLACE TRIGGER TRI_name                         
    before  INSERT OR UPDATE ON table_name               
FOR EACH ROW     
BEGIN
     IF INSERTING THEN     //插入数据操作
        :NEW.createtime := SYSDATE;
    ELSIF UPDATING then    //修改数据操作
        :NEW.createtime := SYSDATE;
    END IF;    
END;