1. In Oracle

2.  A PL/SQL block stored in the database and fired in response to a specified event ◦ DML statements : insert, update, delete ◦ DDL statements : create, alter, drop ◦ Startup or shutdown ◦ An error ◦ A user logon or logoff

3. Create or replace trigger {before|after|Instead of} {Insert | Update | Delete} [of ] On [referencing old as o new as n] [for each row] When ( ) Begin Sql statements End;

4.  Triggering SQL statement  Trigger action  Trigger restriction

5.  DML triggers ◦ Defined on a table and fired in response to an insert, delete or update  DDL triggers ◦ Defined in response to events such as logon or logoff, create alter drop etc.  Instead of triggers ◦ Used for non updateable views

6.  DML trigger definition consists of: ◦ Event that fires the trigger ◦ Database table on which the event occurs ◦ Optional condition controlling when trigger executes  Types: ◦ Row level  Trigger fired or each row updated, inserted or deleted ◦ Statement level  Trigger fired for each sql statement executed

7. create or replace trigger before_update_emp before update on emp begin insert into empcheck values('Before update','Statement', sysdate); dbms_output.put_line('Some updation done on Emp'); end; / Update emp set sal=sal+100; Some updation done on emp 14 rows updated Select * from empcheck; EVENT LEVEL_CHECK DATE_CHEC -------------------- -------------------------------- ------------ ------------------ Before update Statement 13-SEP-13

8. create or replace trigger before_update_row_emp_sal before update of sal on emp For each row begin insert into empcheck values('Before update',’Row', sysdate); dbms_output.put_line('Some updation done on Emp Sal column'); end; / SQL> update emp set sal=sal+10 where deptno=10; Some updation done on Emp Some updation done on Emp Sal column 3 rows updated. SQL> select * from empcheck; EVENT LEVEL_CHECK DATE_CHEC -------------------- ------------------------------ --------- Before update Statement 13-SEP-13 Before update Row 13-SEP-13

9. create or replace trigger display_salary_changes before delete or update or insert on emp for each row declare sal_diff number; begin sal_diff:=:new.sal-:old.sal; dbms_output.put_line('Old salary: '||:old.sal); dbms_output.put_line('New salary: '||:new.sal); dbms_output.put_line('Salary Difference: '||sal_diff); end; /

10. create trigger trig_alter_scott before alter on scott.schema begin raise_application_error(-20000,'Cannot alter any table in scott'); end; / alter table emp drop primary key; ERROR at line 1: ORA-00604: error occurred at recursive SQL level 1 ORA-20000: Cannot alter any table in scott

11.  Help to make non updateable views updateable  Called so because unlike other types of triggers, oracle fires the trigger instead of executing the triggering statement  Exist only on views

12. Create a view create or replace view v as select empno,ename,sal from emp where sal>2000; Create a trigger(Instead of) create or replace trigger emp_trig instead of insert on v begin if :new.sal >2000 then insert into emp (empno,ename,sal) values(:new.empno,:new.ename,:new.sal); else raise_application_error(-20001,'Insertion from this view invalid'); end if; end; /

13.  Creation of a non updateable view Create view vtest as select deptno,sum(sal) as total from emp group by deptno;  Updation through the view not possible update vtest set deptno=20 where deptno=10; ORA-01732: data manipulation operation not legal on this view

14. Creation of Instead of trigger create or replace trigger emp_trig2 instead of update on vtest begin if updating then update emp set deptno=:new.deptno; end if; end; / Updation using trigger update vtest set deptno=20 where deptno=10; 1 row updated.

15.  Mutating table exceptions occur triggering table is referenced from within the row level trigger code  This error is raised when a trigger attempts to execute a DML statement on the same table that the trigger is defined on

16. create or replace trigger trig_up_emp after update on emp for each row declare i number; begin select sum(sal) into i from emp; dbms_output.put_line('The sum of salary of employees is '||i); end; / ERROR at line 1: ORA-04091: table SCOTT.EMP is mutating, trigger/function may not see it ORA-06512: at "SCOTT.TRIG_UP_EMP", line 4 ORA-04088: error during execution of trigger 'SCOTT.TRIG_UP_EMP'

17. create or replace trigger trig_up_emp after update on emp for each row declare i number; pragma autonomous_transaction; begin select sum(sal) into i from emp; dbms_output.put_line('The sum of salary of employees is '||i); commit; end; /

18. View ALL_TRIGGERS, USER_TRIGGERS Alter trigger tigger_name enable; Alter trigger tigger_name disable; Drop trigger trigger_name; Alter table table_name disable all triggers; Alter table table_name enable all triggers;

19.  Refers to SQL statements that are constructed and executed at run time  Execute DDL statements  Manage Ad hoc query and update requirements of web based applications create or replace procedure dynsql_eg(ddl_string varchar2) is begin execute immediate ddl_string; end;