Creating a Trigger : Trigger « Trigger « Oracle PL/SQL Tutorial

1. Oracle PL/SQL Tutorial
2. Trigger
3. Trigger

You create a trigger using the CREATE TRIGGER statement.

The simplified syntax for the CREATE TRIGGER statement is as follows:

CREATE [OR REPLACE] TRIGGER trigger_name
{BEFORE | AFTER | INSTEAD OF} trigger_event
ON table_name
[FOR EACH ROW [WHEN trigger_condition]]
BEGIN
  trigger_body
END trigger_name;

where

1. OR REPLACE specifies the trigger is to replace an existing trigger if present.
2. BEFORE specifies the trigger fires before the triggering event is performed.
3. AFTER specifies the trigger fires after the triggering event is performed.
4. INSTEAD OF specifies the trigger fires instead of performing the triggering event.
5. trigger_event specifies the event that causes the trigger to fire.
6. table_name specifies the table that the trigger references.
7. FOR EACH ROW specifies the trigger is a row-level trigger.
8. A row-level trigger is run for each row when the trigger fires.
9. If you omit FOR EACH ROW, the trigger is a statement-level trigger.
10. A statement-level trigger is run once when the trigger fires regardless of the number of rows affected.
11. trigger_condition specifies a Boolean condition that limits when a trigger actually runs its code.
12. trigger_body contains the SQL and PL/SQL statements that perform the trigger's task.

Quote from:

Oracle Database 10g SQL (Osborne ORACLE Press Series) (Paperback)

# Paperback: 608 pages

# Publisher: McGraw-Hill Osborne Media; 1st edition (February 20, 2004)

# Language: English

# ISBN-10: 0072229810

# ISBN-13: 978-0072229813

SQL>
SQL> CREATE TABLE employee_history (
  2     name VARCHAR2(100),
  3     description VARCHAR2(255),
  4     occurred_on DATE);

Table created.

SQL>
SQL> CREATE TABLE employee_compensation (
  2     company VARCHAR2(100),
  3     name VARCHAR2(100),
  4     compensation NUMBER,
  5     layoffs NUMBER);

Table created.

SQL>
SQL> CREATE OR REPLACE PROCEDURE employee_audit (
  2     name IN VARCHAR2,
  3     description IN VARCHAR2,
  4     occurred_on IN DATE
  5     )
  6  IS
  7     PRAGMA AUTONOMOUS_TRANSACTION;
  8  BEGIN
  9     INSERT INTO employee_history VALUES (
 10        employee_audit.name,
 11        employee_audit.description,
 12        employee_audit.occurred_on
 13        );
 14     COMMIT;
 15  END;
 16  /

Procedure created.

SQL>
SQL>
SQL> CREATE OR REPLACE TRIGGER aft_ins_ceo_comp
  2  AFTER INSERT ON employee_compensation FOR EACH ROW
  3  DECLARE
  4     ok BOOLEAN := FALSE;
  5  BEGIN
  6     IF ok
  7     THEN
  8        employee_audit (
  9           :new.name, 'AFTER INSERT', SYSDATE);
 10     ELSE
 11        RAISE VALUE_ERROR;
 12     END IF;
 13  END;
 14  /

Trigger created.

SQL>
SQL>
SQL> SELECT name,
  2         description,
  3         TO_CHAR (occurred_on, 'MM/DD/YYYY HH:MI:SS') occurred_on
  4    FROM employee_history;

no rows selected

SQL>
SQL> BEGIN
  2     INSERT INTO employee_compensation VALUES ('M', 'J', 9100000, 2700);
  3
  4     INSERT INTO employee_compensation VALUES ('A', 'H', 33200000, 3300);
  5
  6     INSERT INTO employee_compensation VALUES ('E', 'G', 10700000, 20100);
  7
  8  END;
  9  /
BEGIN
*
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error
ORA-06512: at "JAVA2S.AFT_INS_CEO_COMP", line 9
ORA-04088: error during execution of trigger 'JAVA2S.AFT_INS_CEO_COMP'
ORA-06512: at line 2


SQL>
SQL>
SQL> SELECT name,
  2         description,
  3         TO_CHAR (occurred_on, 'MM/DD/YYYY HH:MI:SS') occurred_on
  4    FROM employee_history;

no rows selected

SQL>
SQL>
SQL>
SQL> DROP TABLE employee_compensation;

Table dropped.

SQL>
SQL> DROP TABLE employee_history;

Table dropped.

SQL>