oracle基础教程之触发器（DML触发器的作用）

举个例子

--开发示例1

SQL> CREATE OR REPLACE TRIGGER emp_trigger1
  2  BEFORE INSERT OR UPDATE OR DELETE
  3  ON emp
  4  BEGIN
  5     IF to_char(sysdate,'day') IN ('星期六','星期日')THEN
  6        RAISE_APPLICATION_ERROR(-20006,'不能在休息日改变员工信息！');
  7     END IF;
  8  END;
  9  /
Trigger created

SQL> delete from emp where empno = 7788;
delete from emp where empno = 7788
ORA-20006: 不能在休息日改变员工信息！
ORA-06512: 在 "SCOTT.EMP_TRIGGER1", line 3
ORA-04088: 触发器 'SCOTT.EMP_TRIGGER1' 执行过程中出错

--开发示例2

--创建审计表
CREATE TABLE delete_emp_audit(
       name VARCHAR2(10),
       delete_time DATE
);

--创建触发器
CREATE OR REPLACE TRIGGER del_emp_trigger
AFTER DELETE ON emp
FOR EACH ROW
BEGIN
  INSERT INTO delete_emp_audit VALUES(:old.ename,SYSDATE);
END;

--测试
DELETE FROM emp WHERE empno = 7499;

select * from delete_emp_audit;

--开发示例3
SQL> CREATE OR REPLACE TRIGGER tr_check_sal
  2  BEFORE UPDATE OF sal ON emp
  3  FOR EACH ROW
  4  WHEN (new.salold.sal*1.5)
  5  BEGIN
  6       RAISE_APPLICATION_ERROR(-20028,'工资只升不降，并且升幅不能超过50%');
  7  END;
  8  /
Trigger created

SQL> UPDATE emp SET sal = sal*1.8 WHERE empno = 7788;
UPDATE emp SET sal = sal*1.8 WHERE empno = 7788
ORA-20028: 工资只升不降，并且升幅不能超过50%
ORA-06512: 在 "SCOTT.TR_CHECK_SAL", line 2
ORA-04088: 触发器 'SCOTT.TR_CHECK_SAL' 执行过程中出错

--开发示例4
CREATE OR REPLACE TRIGGER upd_cascade_trigger
AFTER UPDATE OF deptno
ON dept
FOR EACH ROW
BEGIN
  UPDATE emp SET deptno = :new.deptno WHERE deptno = :old.deptno;
END;

--测试
UPDATE dept SET deptno = 50 WHERE deptno = 10;

select deptno,ename from emp where deptno = 50;

oracle基础教程之触发器（DML触发器的作用）

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