Examples: Triggers (PL/SQL)

The following example shows a before row-level trigger that calculates the commission of every new employee belonging to department 30 before a record for that employee is inserted into the EMP table:

CREATE OR REPLACE TRIGGER emp_comm_trig
    BEFORE INSERT ON emp
    FOR EACH ROW
BEGIN
    IF :NEW.deptno = 30 THEN
        :NEW.comm := :NEW.sal * .4;
    END IF;
END;

The trigger computes the commissions for two new employees and inserts those values as part of the new employee rows:

INSERT INTO emp VALUES (9005,'ROBERS','SALESMAN',7782,SYSDATE,3000.00,NULL,30);

INSERT INTO emp VALUES (9006,'ALLEN','SALESMAN',7782,SYSDATE,4500.00,NULL,30);

SELECT * FROM emp WHERE empno IN (9005, 9006);

     EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
      9005 ROBERS     SALESMAN        7782 01-APR-05       3000       1200         30
      9006 ALLEN      SALESMAN        7782 01-APR-05       4500       1800         30

The following example shows three after row-level triggers.

• When a new employee row is inserted into the EMP table, one trigger (EMP_INS_TRIG) adds a new row to the JOBHIST table for that employee and adds a row to the EMPCHGLOG table with a description of the action.
• When an existing employee row is updated, the second trigger (EMP_CHG_TRIG) sets the ENDDATE column of the latest JOBHIST row (assumed to be the one with a null ENDDATE) to the current date and inserts a new JOBHIST row with the employee's new information. This trigger also adds a row to the EMPCHGLOG table with a description of the action
• When an employee row is deleted from the EMP table, the third trigger (EMP_DEL_TRIG) adds a row to the EMPCHGLOG table with a description of the action.

CREATE TABLE empchglog (
    chg_date        DATE,
    chg_desc        VARCHAR2(30)
);
CREATE OR REPLACE TRIGGER emp_ins_trig
    AFTER INSERT ON emp
    FOR EACH ROW
DECLARE
    v_empno         emp.empno%TYPE;
    v_deptno        emp.deptno%TYPE;
    v_dname         dept.dname%TYPE;
    v_action        VARCHAR2(7);
    v_chgdesc       jobhist.chgdesc%TYPE;
BEGIN
    v_action := 'Added';
    v_empno := :NEW.empno;
    v_deptno := :NEW.deptno;
    INSERT INTO jobhist VALUES (:NEW.empno, SYSDATE, NULL,
        :NEW.job, :NEW.sal, :NEW.comm, :NEW.deptno, 'New Hire');

    INSERT INTO empchglog VALUES (SYSDATE,
        v_action || ' employee # ' || v_empno);
END;

CREATE OR REPLACE TRIGGER emp_chg_trig
    AFTER UPDATE ON emp
    FOR EACH ROW
DECLARE
    v_empno         emp.empno%TYPE;
    v_deptno        emp.deptno%TYPE;
    v_dname         dept.dname%TYPE;
    v_action        VARCHAR2(7);
    v_chgdesc       jobhist.chgdesc%TYPE;
BEGIN
    v_action := 'Updated';
    v_empno := :NEW.empno;
    v_deptno := :NEW.deptno;
    v_chgdesc := '';
    IF NVL(:OLD.ename, '-null-') != NVL(:NEW.ename, '-null-') THEN
        v_chgdesc := v_chgdesc || 'name, ';
    END IF;
    IF NVL(:OLD.job, '-null-') != NVL(:NEW.job, '-null-') THEN
        v_chgdesc := v_chgdesc || 'job, ';
    END IF;
    IF NVL(:OLD.sal, -1) != NVL(:NEW.sal, -1) THEN
        v_chgdesc := v_chgdesc || 'salary, ';
    END IF;
    IF NVL(:OLD.comm, -1) != NVL(:NEW.comm, -1) THEN
        v_chgdesc := v_chgdesc || 'commission, ';
    END IF;
    IF NVL(:OLD.deptno, -1) != NVL(:NEW.deptno, -1) THEN
        v_chgdesc := v_chgdesc || 'department, ';
    END IF;
    v_chgdesc := 'Changed ' || RTRIM(v_chgdesc, ', ');
    UPDATE jobhist SET enddate = SYSDATE WHERE empno = :OLD.empno
        AND enddate IS NULL;
    INSERT INTO jobhist VALUES (:NEW.empno, SYSDATE, NULL,
        :NEW.job, :NEW.sal, :NEW.comm, :NEW.deptno, v_chgdesc);

    INSERT INTO empchglog VALUES (SYSDATE,
        v_action || ' employee # ' || v_empno);
END;

CREATE OR REPLACE TRIGGER emp_del_trig
    AFTER DELETE ON emp
    FOR EACH ROW
DECLARE
    v_empno         emp.empno%TYPE;
    v_deptno        emp.deptno%TYPE;
    v_dname         dept.dname%TYPE;
    v_action        VARCHAR2(7);
    v_chgdesc       jobhist.chgdesc%TYPE;
BEGIN
    v_action := 'Deleted';
    v_empno := :OLD.empno;
    v_deptno := :OLD.deptno;

    INSERT INTO empchglog VALUES (SYSDATE,
        v_action || ' employee # ' || v_empno);
END;

In the following example, two employee rows are added using two separate INSERT statements, and then both rows are updated using a single UPDATE statement. The JOBHIST table shows the action of the trigger for each affected row: two new hire entries for the two new employees and two changed commission records. The EMPCHGLOG table also shows that the trigger was fired a total of four times, once for each action against the two rows.

INSERT INTO emp VALUES (9003,'PETERS','ANALYST',7782,SYSDATE,5000.00,NULL,40);

INSERT INTO emp VALUES (9004,'AIKENS','ANALYST',7782,SYSDATE,4500.00,NULL,40);

UPDATE emp SET comm = sal * 1.1 WHERE empno IN (9003, 9004);

SELECT * FROM jobhist WHERE empno IN (9003, 9004);

     EMPNO STARTDATE ENDDATE   JOB              SAL       COMM     DEPTNO CHGDESC
---------- --------- --------- --------- ---------- ---------- ---------- ------------------
      9003 31-MAR-05 31-MAR-05 ANALYST         5000                    40 New Hire
      9004 31-MAR-05 31-MAR-05 ANALYST         4500                    40 New Hire
      9003 31-MAR-05           ANALYST         5000       5500         40 Changed commission
      9004 31-MAR-05           ANALYST         4500       4950         40 Changed commission

SELECT * FROM empchglog;

CHG_DATE  CHG_DESC
--------- ------------------------------
31-MAR-05 Added employee # 9003
31-MAR-05 Added employee # 9004
31-MAR-05 Updated employee # 9003
31-MAR-05 Updated employee # 9004

After both employees are deleted with a single DELETE statement, the EMPCHGLOG table shows that the trigger was fired twice, once for each deleted employee:

DELETE FROM emp WHERE empno IN (9003, 9004);

SELECT * FROM empchglog;

CHG_DATE  CHG_DESC
--------- ------------------------------
31-MAR-05 Added employee # 9003
31-MAR-05 Added employee # 9004
31-MAR-05 Updated employee # 9003
31-MAR-05 Updated employee # 9004
31-MAR-05 Deleted employee # 9003
31-MAR-05 Deleted employee # 9004