DatabaseTrigger:(It cannot be used in Application i.e
frontend):-----------------------------------------------------------------------------------Database
Trigger is Event Based database Object From PL/SQL. This Object is
used to apply business rules on database. Business rules are user
specific validation.Database Trigger execution is decided by Oracle
server based on the event defined for trigger. These events are
(i.e)Database Events are categorised into four
groups:-------------------------------------------------------------------1)DML
Events:(Used On Table)-INSERT-UPDATE-DELETE2)Instead Of Event (Used
On view)3)DDL Events:(Used On Any Database
Object)-CREATE-ALTER-DROP4)Database Events:-After Startup-Before
Shutdown-After Login-Before Logout-ON Server Error.DML
Triggers:==========*)Are Used to protect Data Manipulation on
tables.*)DML Triggers have:-->Two Execution Time --> BEFORE
/AFTER EVENT--> Three Events (INSERT or DELETE or UPDATE)(
INSERT or DELETE)( INSERT or UPDATE)(UPDATE or DELETE)-->Two
Types (Statement Trigger(table level trigger) / Row Trigger)-->
Trigger Condition:(is not allowed for Table Trigger) If the trigger
is row trigger it is executed. If trigger condition is True,then
only trigger body (Anonymous Block) is processed.*) For DML Trigger
PL/SQL provides Three variables to know the Current Event :They
are-->INSERTING-->DELETING-->UPDATINGall the above are
boolean variables and any one will be true.*)For Row Trigger Server
Provides Two variables and they keep current record values. These
variables are :--> OLD(%ROWTYPE of table)--> NEW(%ROWTYPE of
table)OLD-->keeps value for cuurent record from table.NEW -->
keeps value for current record from user.OLD
NEW----------------------INSERT x okDELETE ok xUPDATE ok okDML
Trigger Syntax:-----------------------------CREATE [OR REPLACE]
TRIGGER BEFORE / AFTERINSERT OR DELETE OR UPDATE ON [FOR EACH
ROW[WHEN ()]];How To Raise Error for Oracle
Server:---------------------------------------------------Syntax:RAISE_APPLICATION_ERROR(,);
Note:Error Code must be between -20,000 and -20,999.Q)Check
employee table against Data Manipulation as per the
-----------------------------------------------------------------------------------following
Criteria:------------------------->Insert shoud be allowed
before 12'O clock-->Delete should not be allowed before 12'O
clock--> Update should not be allowed before 9.00 amafter 5.00
pm.sol):CREATE OR REPLACE TRIGGER Check_EmpBEFORE INSERT OR DELETE
OR UPDATE ON empDECLARE vSeconds NUMBER
:=(To_Char(sysdate,'hh24')*3600) + (To_Char(sysdate,'mi')*60) +
To_Char(sysdate,'ss');BEGIN IF INSERTING=true AND vSeconds <
(12*3600) THENRaise_Application_Error (-20001,'Insert Not allowed
before 12 Noon'); ELSIF DELETING =true AND vSeconds > (12*3600)
THENRaise_Application_Error (-20002,'Delete Not allowed after 12
Noon'); ELSIF UPDATING =true AND vSeconds NOT BETWEEN (9*3600) AND
(17*3600) THENRaise_Application_Error (-20003,'No Update before 9
am after 5pm'); END IF;END;/Checking:-------------SQL> Delete
emp;Delete emp *ERROR at line 1:ORA-20002: Delete Not allowed after
12 NoonORA-06512: at "SIVA1.CHECK_EMP", line 10ORA-04088: error
during execution of trigger 'SIVA1.CHECK_EMP'SQL> Update emp set
sal=2000;Update emp set sal=2000 *ERROR at line 1:ORA-20003: No
Update before 9 am after 5pmORA-06512: at "SIVA1.CHECK_EMP", line
14ORA-04088: error during execution of trigger
'SIVA1.CHECK_EMP'Note:------If check requires any data from the
table then it is row trigger.or validations values are comming from
table is is row trigger.or otherwise it is statement
trigger.Q2)Protect employee table -for insert of new records for
manager and president.-delete should not be allowed for who joiner
after year 80-update should not be allowed for salaryCREATE OR
REPLACE TRIGGER Check_EmpBEFORE INSERT OR DELETE OR UPDATE ON
empFOR EACH ROWBEGIN IF INSERTING=true AND :NEW.job
IN('MANAGER','PRESIDENT') THENRaise_Application_Error (-20001,'No
Insert For Manager And President'); ELSIF DELETING =true AND
To_Char(:OLD.hiredate,'yy') > 80 THENRaise_Application_Error
(-20002,'No delete for employee joined after 80'); ELSIF UPDATING
=true AND NVL(:OLD.sal,0)NVL(:NEW.sal,0)
THENRaise_Application_Error (-20003,'No Update for salary'); END
IF;END;/execution:-------------SQL> drop trigger
Check_Emp;Trigger dropped.Trigger Created SQL> update emp set
sal=4000;update emp set sal=4000 *ERROR at line 1:ORA-20003: No
Update for salaryORA-06512: at "SIVA1.CHECK_EMP", line 12ORA-04088:
error during execution of trigger 'SIVA1.CHECK_EMP'SQL> CREATE
TABLE deptback 2 as 3 SELECT * FROM dept WHERE 1=2;Table
created.Note: For deleted records we have to dump in a separate
table.For that we need another trigger i.e given below.CREATE OR
REPLACE TRIGGER Backup_DeptAFTER DELETE ON deptFOR EACH ROWBEGIN
INSERT INTO deptback(deptno,dname,loc)
VALUES(:OLD.deptno,:OLD.dname,:old.loc);END;/Note: ------Maximum
Number of Triggers on a
table:------------------------------------------------------BEFORE
INSERT FOR STATEMENTAFTER INSERT FOR STATEMENTBEFORE DELETE FOR
STATEMENTAFTER DELETE FOR STATEMENTBEFORE UPDATE FOR STATEMENTAFTER
UPDATE FOR STATEMENTBEFORE INSERT FOR ROWLEVELAFTER INSERT FOR
ROWLEVELBEFORE DELETE FOR ROWLEVELAFTER DELETE FOR ROWLEVELBEFORE
UPDATE FOR ROWLEVELAFTER UPDATE FOR ROWLEVELInstead Of
Trigger:==============*)This Trigger is used on view Object to
allow data manipulation on the base table(s).*)Within the trigger
we have to write DML commands to manipulate the base table(s)*)This
trigger always fire BEFORE the event and it is always ROW
TRIGGER.Instead Of Trigger
Syntax:---------------------------------CREATE [OR REPLACE] TRIGGER
INSTEAD OF INSERT OR DELETE OR UPDATEON FOR EACH ROW[WHEN
();Note:------A table can have maximum of three triggers.*)First
Create a view:---------------------------CREATE VIEW v1ASSELECT
emp.empno,emp.ename,dept.deptno,dept.dnameFROM emp,deptWHERE
emp.deptno=dept.deptno;check:DELETE FROM v1;INSERT INTO v1
values(1,'aa',10,'sales');*)Create trigger on
view:-------------------------------CREATE OR REPLACE TRIGGER
ins1INSTEAD OF INSERT ON v1FOR EACH ROWBEGINIF
Check_empno(:NEW.empno) =1 THEN Raise_application_Error
(-20001,'Duplicate Empno');END IF;--IF Check_deptno(:NEW.deptno) =1
THEN INSERT INTO dept(deptno,dname)
VALUES(:NEW.deptno,:NEW.dname);END IF;--INSERT INTO
emp(empno,ename,deptno)
VALUES(:NEW.empno,:NEW.ename,:new.deptno);END;*)To Delete records
From view:------------------------------------------CREATE OR
REPLACE FUNCTION Count_emp_for_deptno(pDeptno IN NUMBER) RETURN
NUMBERIS vTemp NUMBER;BEGIN SELECT COUNT(*) INTO vTemp FROM emp
WHERE deptno=pDeptno; RETURN (vTemp);END
Count_emp_for_deptno;checking:------------SQL> SELECT
Count_emp_for_deptno(10) FROM
Dual;COUNT_EMP_FOR_DEPTNO(10)------------------------ 4CREATE OR
REPLACE TRIGGER del1INSTEAD OF DELETE ON v1FOR EACH ROWBEGINDELETE
FROM EMPWHERE empno=:OLD.empno;IF
Count_emp_for_deptno(:OLD.deptno)=0THENDELETE FROM deptWHERE
deptno=:OLD.deptno;END IF;END;/*)Updating the view using
trigger:---------------------------------------------CREATE OR
REPLACE TRIGGER upd1INSTEAD OF UPDATE ON v1FOR EACH ROWBEGIN UPDATE
emp SETename= :NEW.ename;deptno= :NEW.deptnoWHERE empno=
:OLD.empno;--UPDATE dept SETdname= :NEW.dnameWHERE deptno=
:=OLD.deptno;END;/
