Oracle 触发器详解 5

8.6 数据库触发器的应用实例
　　用户可以使用数据库触发器实现各种功能：
　　复杂的审计功能；
　　例：将EMP 表的变化情况记录到AUDIT_TABLE和AUDIT_TABLE_VALUES中。
CREATE TABLE audit_table(
Audit_id NUMBER,
User_name VARCHAR2(20),
Now_time DATE,
Terminal_name VARCHAR2(10),
Table_name VARCHAR2(10),
Action_name VARCHAR2(10),
Emp_id NUMBER(4));

CREATE TABLE audit_table_val(
Audit_id NUMBER,
Column_name VARCHAR2(10),
Old_val NUMBER(7,2),
New_val NUMBER(7,2));

CREATE SEQUENCE audit_seq
START WITH 1000
INCREMENT BY 1
NOMAXVALUE
NOCYCLE NOCACHE;

CREATE OR REPLACE TRIGGER audit_emp
AFTER INSERT OR UPDATE OR DELETE ON emp
FOR EACH ROW
DECLARE
Time_now DATE;
Terminal CHAR(10);
BEGIN
Time_now:=sysdate;
Terminal:=USERENV('TERMINAL');
IF INSERTING THEN
INSERT INTO audit_table
VALUES(audit_seq.NEXTVAL, user, time_now,
terminal, 'EMP', 'INSERT', :new.empno);
ELSIF DELETING THEN
INSERT INTO audit_table
VALUES(audit_seq.NEXTVAL, user, time_now,
terminal, 'EMP', 'DELETE',ld.empno);
ELSE
INSERT INTO audit_table
VALUES(audit_seq.NEXTVAL, user, time_now,
terminal, 'EMP', 'UPDATE',ld.empno);
IF UPDATING('SAL') THEN
INSERT INTO audit_table_val
VALUES(audit_seq.CURRVAL, 'SAL',ld.sal, :new.sal);
ELSE UPDATING('DEPTNO')
INSERT INTO audit_table_val
VALUES(audit_seq.CURRVAL, 'DEPTNO',ld.deptno, :new.deptno);
END IF;
END IF;
END;
　　增强数据的完整性管理；
　　例：修改DEPT表的DEPTNO列时，同时把EMP表中相应的DEPTNO也作相应的修改；
CREATE SEQUENCE update_sequence
INCREMENT BY 1
START WITH 1000
MAXVALUE 5000 CYCLE;

ALTER TABLE emp
ADD update_id NUMBER;

CREATE OR REPLACE PACKAGE integritypackage AS
Updateseq NUMBER;
END integritypackage;

CREATE OR REPLACE PACKAGE BODY integritypackage AS
END integritypackage;

CREATE OR REPLACE TRIGGER dept_cascade1
BEFORE UPDATE OF deptno ON dept
DECLARE
Dummy NUMBER;
BEGIN
SELECT update_sequence.NEXTVAL INTO dummy FROM dual;
Integritypackage.updateseq:=dummy;
END;

CREATE OR REPLACE TRIGGER dept_cascade2
AFTER DELETE OR UPDATE OF deptno ON dept
FOR EACH ROW
BEGIN
IF UPDATING THEN
UPDATE emp SET deptno=:new.deptno,
update_id=integritypackage.updateseq
WHERE emp.deptno=:old.deptno AND update_id IS NULL;
END IF;
IF DELETING THEN
DELETE FROM emp
WHERE emp.deptno=:old.deptno;
END IF;
END;

CREATE OR REPLACE TRIGGER dept_cascade3
AFTER UPDATE OF deptno ON dept
BEGIN
UPDATE emp SET update_id=NULL
WHERE update_id=integritypackage.updateseq;
END;

SELECT * FROM EMP ORDER BY DEPTNO;
UPDATE dept SET deptno=25 WHERE deptno=20;
　　帮助实现安全控制；
　　例：保证对EMP表的修改仅在工作日的工作时间；
CREATE TABLE company_holidays(day DATE);

INSERT INTO company_holidays
VALUES(sysdate);
INSERT INTO company_holidays
VALUES(TO_DATE('21-10月-01', 'DD-MON-YY'));

CREATE OR REPLACE TRIGGER emp_permit_change
BEFORE INSERT OR DELETE OR UPDATE ON emp
DECLARE
Dummy NUMBER;
Not_on_weekends EXCEPTION;
Not_on_holidays EXCEPTION;
Not_working_hours EXCEPTION;
BEGIN
/* check for weekends */
IF TO_CHAR(SYSDATE, 'DAY') IN ('星期六', '星期日') THEN
RAISE not_on_weekends;
END IF;
/* check for company holidays */
SELECT COUNT(*) INTO dummy FROM company_holidays
WHERE TRUNC(day)=TRUNC(SYSDATE);
IF dummy >0 THEN
RAISE not_on_holidays;
END IF;
/* check for work hours(8:00 AM to 18:00 PM */
IF (TO_CHAR(SYSDATE,'HH24')<8 OR TO_CHAR(SYSDATE, 'HH24')>18) THEN
RAISE not_working_hours;
END IF;
EXCEPTION
WHEN not_on_weekends THEN
RAISE_APPLICATION_ERROR(-20324,
'May not change employee table during the weekends');
WHEN not_on_holidays THEN
RAISE_APPLICATION_ERROR(-20325,
'May not change employee table during a holiday');
WHEN not_working_hours THEN
RAISE_APPLICATION_ERROR(-20326,
'May not change employee table during no_working hours');
END;

    例：更新T_PARAMETER表中的某些行时，同步更新t_version表：
create or replace
TRIGGER TR_SYS_PARAMETER_VER_SYN
AFTER UPDATE OF PARAMETER_VALUE
ON T_PARAMETER
FOR EACH ROW
WHEN (old.PARAMETER_NAME='alarm_gps_interval_time' or
      old.PARAMETER_NAME='taxi_server_ip' or
      old.PARAMETER_NAME='taxi_server_port' or
      old.PARAMETER_NAME='sys_transfer_time' or
      old.PARAMETER_NAME='enable_card_bin_type' or
      old.PARAMETER_NAME='normal_gps_interval_time')
BEGIN

    IF :NEW.PARAMETER_VALUE !=ld.PARAMETER_VALUE THEN
       update t_version
       set version_value=to_char(sysdate,'yyyymmdd')
       where version_name='system_parameter_version';
    END IF;
END;