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', :old.empno);
ELSE
INSERT INTO audit_table
VALUES(audit_seq.NEXTVAL, user, time_now,
terminal, 'EMP', 'UPDATE', :old.empno);
IF UPDATING('SAL') THEN
INSERT INTO audit_table_val
VALUES(audit_seq.CURRVAL, 'SAL', :old.sal, :new.sal);
ELSE UPDATING('DEPTNO')
INSERT INTO audit_table_val
VALUES(audit_seq.CURRVAL, 'DEPTNO', :old.deptno, :new.deptno);
END IF;
END IF;
END;
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', :old.empno);
ELSE
INSERT INTO audit_table
VALUES(audit_seq.NEXTVAL, user, time_now,
terminal, 'EMP', 'UPDATE', :old.empno);
IF UPDATING('SAL') THEN
INSERT INTO audit_table_val
VALUES(audit_seq.CURRVAL, 'SAL', :old.sal, :new.sal);
ELSE UPDATING('DEPTNO')
INSERT INTO audit_table_val
VALUES(audit_seq.CURRVAL, 'DEPTNO', :old.deptno, :new.deptno);
END IF;
END IF;
END;
