1. Triggers

2. Triggers
A database trigger is a stored procedure that is fired when an insert, update or delete statement is issued against the associated table.

3. Database triggers can be used for the following purposes.
To generate data automatically.
To enforce complex integrity constraints. (e.g. checking with sysdate, checking with data in another table).
To customize complex security authorizations.
To maintain replicate tables.
To audit data modifications.

4. Syntax Create or replace trigger <trigger_name>
[before / after] [insert/update/delete] on <tablename> [for each statement / for each row] [when <condition>];

5. Parts of trigger
Trigger statement
Trigger body
Trigger restriction

6. Trigger statement Trigger body Trigger Restriction
The trigger statement specifies the DML statements like update, delete and insert and it fires the trigger body. It also specifies the table to which the trigger is associated.
Trigger body
Trigger body is a PL/SQL block that is executed when a triggering statement is issued.
Trigger Restriction
Restrictions on a trigger can be achieved using the WHEN clause as shown in the syntax for creating triggers. They can be included in the definition of a row trigger, wherein, the condition in the

7. Types of triggers Before After For each row
For each statement (default)

8. Example
SQL> ed
create or replace trigger t_emp before insert or update
on emp for each row
declare
cursor st is select eno from salesman;
begin
if :new.ename is null then
raise_application_error(-20001,'NULL NOT ALLOWED');
end if;
end;
SQL> /
Trigger created.
SQL> insert into emp values('');
insert into emp values('') *
ERROR at line 1:
ORA-20001: NULL NOT ALLOWED
ORA-06512: at "ME05.DATVALID", line 5
ORA-04088: error during execution of trigger 'ME12.DATVALID'

9. Example -2
SQL> create or replace trigger trigger4
after delete on dept for each row
begin
delete from emp where dno=:old.dno;
end;
SQL> delete from dept where dno=10;
SQL> Select * from dept;
SQL> Select * from emp;

10. SQL> create table dml_tab (action varchar(15), atime date);
SQL> alter SESSION NET NLS_DATE_FORMAR=‘DD-MON-YYYY HH24:MI:SS’;
SQL> create or replace trigger tigger5
After insert or delete or update on emp
Begin
If inserting then
Insert into dml_tab values (‘INSERT’, sysdate);
End if;
If deleting then
Insert into dml_tab values (‘DELETE’, sysdate);
If updating (salary) then
Insert into dml_tab values (‘UPDATE’, sysdate);
End;
SQL > insert into emp values ( 101,’Raja’, 20000,10,300);
SQL> delete emp where eno=100;
SQL> update emp set salary=25000 where eno=200;
SQL> select * from dml_tab;

11. Client/Server Systems
Networked computing model
Processes distributed between clients and servers
Client–Workstation (usually a PC) that requests and uses a service
Server–Computer (PC/mini/mainframe) that provides a service
For DBMS, server is a database server

12. database server architecture