This document discusses database triggers in Oracle. It defines a trigger as a statement that is automatically executed by the system in response to data modifications. The key components of a trigger are the trigger statement, which fires the trigger body, and the trigger body, which is a PL/SQL block that runs when the triggering statement is issued. Triggers can be defined as before or after triggers, and at the row or statement level. Built-in triggers can be created for events like server errors, logons, and logoffs. Examples are provided for creating before and after row-level triggers.

2. This is executed automatically by the system as a side effect of a modification to the data base.

3. Example Atm card, on-line reservation.

4. Compopnents Trigger Trigger statement: The DML statement(insert,update,delete) is called the trigger statement. It fires the trigger body. Trigger body: The pl/sql block that is executed when a triggering statement is issued is called the trigger body. Trigger Restriction: This is on optional part. The restriction is imposed using when clause and is applicable only for row triggers.

6. After

7. For each row

10. Insert

11. Update

14. Log on  trigger will be fired after the client application logs on to the database successfully.

17. create or replace trigger rowins1 before insert on branch

18. declare

19. x number;

20. begin

21. select count(*) into x from branch;

22. dbms_output.put_line(' number of available records before insert :' ||x);

24. output:

27. create or replace trigger rowins2 after insert on branch

28. declare

29. x number;

30. begin

31. select count(*) into x from branch;

32. dbms_output.put_line(' number of available records after insert :' ||x);

34. number of available records before insert :4 number of available records after insert :5 1 row created.

35. alter trigger rowins1 disable;

36. Trigger altered.

37. insert into branch values('east',1450000,'nellai')

38. number of available records after insert :6

40. select trigger_name,trigger_body from user_triggers;

41. Parts of trigger Trigger statement Trigger body Trigger restriction

42. Data base trigger A database trigger is a stored procedure. It is fired implicitly when an insert,update or delete statements are issued against the table on which the trigger is defined

43. Purpose of trigger To enforce complex integrity constraints. To enforce complex business rules. To maintain a replicate table. To generate data automatically To avoid invalid transaction

44. Department of CE/ITMSPVL Polytechnic College Pavoorchatram