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Triggers are simply stored procedures that are ran automatically by the

database whenever some e vent (usually a table up date) happens .

Triggers are basically PL/SQL procedure s that are associated with tables,

and are called whenever a certain modification (event) occurs. The

modification statements may include INSERT, UPDATE, and DELETE.

Trigger: procedure that starts automatically if specified

changes occur to the DBMS

Three parts:

Event (activates the trigger)

Condition (tests whether the triggers should run)

Action (what happens if the trigger runs)

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The general structure of triggers is:CREATE [OR REPLACE]

TRIGGER trigger name

BEFORE (or AFTER)

INSERT OR UPDATE [OF COLUMNS] OR DELETEON table name

[FOR EACH ROW [WHEN (condition)]]

BEGIN

...

END;

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Sample Table to b e Triggered

CREATE TABLE PERSON

(ID INT,

NAME VARCHAR(30),DOB DATE,

PRIMARY KEY(ID)

);

1.Before Insert Trigger

We write a trigger tofire before the insert take s place.

CREATE OR REPLACE

TRIGGER PERSON_INSERT_BEFORE

BEFORE

INSERTON PERSON

FOR EACH ROW

BEGIN

DBMS_OUTPUT.PUT_LINE(BEFORE INSERT OF ||

:NEW.NAME);

END;

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Now let us test it out:

INSERT INTO PERSON(ID,NAME,DOB) VALUES (1,JOHN DOE,SYSDATE);

The single INSERT statement fires the trigger. When we run it, we get the print

out of BEFORE INSERT OF JOHN DOE. I e:

2. After Insert Trigger

CREATE OR REPLACE

TRIGGER PERSON_INSERT_AFTER

AFTER

INSERT

ON PERSON

FOR EACH ROW

BEGINDBMS_OUTPUT.PUT_LINE(AFTER INSERT OF ||

:NEW.NAME);

END;

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And with our 2nd test INSERT

INSERT INTO PERSON(ID,NAME,DOB) VALUES

(2,JANE DOE,SYSDATE);For a total result of:

INSERT INTO PERSON(ID,NAME,DOB) VALUES (2,JANE

DOE,SYSDATE);

BEFORE INSERT OF JANE DOE

AFTER INSERT OF JANE DOE

Notice that both triggers have fired.

One before the INSERT the other one after

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3.Before Up date Statement Trigger

Now that we have some data in the table, we can create an up date

trigger, that would fire whenever someone tries to up date any

person (or persons).

CREATE OR REPLACE

TRIGGER PERSON_UPDATE_S_BEFORE

BEFORE UPDATE

ON PERSON

BEGIN

DBMS_OUTPUT.PUT_LINE(BEFORE UPDATING SOME PERSON(S));

END;

Now , lets run an up date...

UPDATE PERSON SET DOB = SYSDATE;

Which produces the result:

SQL> UPDATE PERSON SET DOB = SYSDATE;

BEFORE UPDATING SOME PERSON(S)

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Special IF statements

Inside the P L/SQL block of a trigger we can use if statements to

determine what statement caused the firing of the trigger. These aregenerally of the form:

IF inserting THEN...where besides inserting you c an also use

updating and deleting. An example would be something like:

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CREATE OR REPLACE

TRIGGER PERSON_BIUD

BEFORE INSERT OR UPDATE OR DELETE ON PERSON

FOR EACH ROWBEGIN

IF INSERTING THEN

DBMS_OUTPUT.PUT_LINE(INSERTING PERSON: ||

:NEW.NAME);ELSIF UPDATING THEN

DBMS_OUTPUT.PUT_LINE(UPDATING PERSON: ||

:OLD.NAME || TO || :NEW.NAME);

ELSIF DELETING THEN

DBMS_OUTPUT.PUT_LINE(DELETING PERSON: ||

:OLD.NAME);

END IF;

END;

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Notice that we only have one TRIGGER, and we are using IF

statements to determine what statement invoked it, and

display an appropriate message in various cases. For example,

when we do an insert:

INSERT INTO PERSON(ID,NAME,DOB) VALUES

(3,SUPERMAN,TO_DATE(09/05/1950,MM/DD/YYYY))

Then we get output like:

INSERTING PERSON: SUPERMAN

If we go ahead and modify that person:

UPDATE PERSON SET NAME = BATMAN WHERE NAME =

SUPERMAN;

Then we get an output like:

UPDATING PERSON: SUPERMAN TO BATMAN

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And finally , if we go ahead and delete that person:

DELETE PERSON WHERE NAME = BATMAN;

Then we would get output like:DELETING PERSON: BATMAN

Dropping Triggers

You c an DROP triggers j us t like anything. The general format

would b e something like :

DROP TRIGGER triggername;

In order to disable trigger

ALTER TRIGGER PERSON_DOB DISABLE;

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Just like any other procedural language, PL/SQL has code fragments that

are called PROCEDURES.

You can call these PROCEDURES from other code fragments, or directly

from SQL*Plus

Procedures are code fragments that dont normally return a value, but

may have some outside effects (like updating tables). The generalformat of a procedure is :

PROCEDURE procedure_name IS

BEGINprocedure_body

END;

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For example, to create (or re place ) a HELLO

procedure, you might do something like this:

CREATE OR REPLACE

PROCEDURE HELLO IS

BEGIN

DBMS_OUTPUT.PUT_LINE(Hello

World);END;

BEGIN

HELLO();

END;

Or you can s imply execute it in SQL*Plus

by typing:

CALL HELLO();

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CREATE OR REPLACE

PROCEDURE DISPN (N INT) IS

BEGIN

DBMS_OUTPUT.PUT_LINE(N is || N);END;

Which if you c all, will promptly dis

play:

SQL> CALL DISPN(1234567891);

N is 1234567891

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You can also have multiple parameters. For example, you can accept

A and B and display their sum and product.

CREATE OR REPLACE

PROCEDURE DISP_AB (A INT, B INT) IS

BEGIN

DBMS_OUTPUT.PUT_LINE(A + B = || (A + B));DBMS_OUTPUT.PUT_LINE(A * B = || (A * B));

END;

Which when ran, displays

something like (de p ending on thevalues you provide ):

SQL> CALL DISP_AB(17,23);

A + B = 40

A * B = 391

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IN, OUT , IN OUT

CREATE OR REPLACE

PROCEDURE DOUBLEN (N IN OUT

INT) IS

BEGIN

N := N * 2;

END;

To run it, we also create a s mall c o

de fragment:

DECLARER INT;

BEGIN

R := 7;

DBMS_OUTPUT.PUT_LINE(BEFORECALL R IS: || R);

DOUBLEN(R);

DBMS_OUTPUT.PUT_LINE(AFTER

CALL R IS: || R);

END;

Which w hen ran displays:

BEFORE CALL R IS: 7

AFTER CALL R IS: 14

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Dropping Procedures

If youre interested in getting rid of a procedure totally, you can

DROP it.The general format of a DROP is:

DROP PROCEDURE procedure_name;

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FunctionsFunctions are special types of procedure s that have the capability to

return a value.

The general format of a function is very similar to the general

format of a procedure:

CREATE OR REPLACE

FUNCTION function name (functionparams) RETURN return_typeIS

BEGIN

function_body

RETURN something_of_return_type;END;

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For example, to write a function that computes the s um of two

numbers, you might do something like this:

CREATE OR REPLACEFUNCTION ADD_TWO (A INT,B INT) RETURN INT IS

BEGIN

RETURN (A + B);

END;

To run it, well w rite a small piece of co de that calls this:

BEGIN

DBMS_OUTPUT.PUT_LINE(RESULT IS: || ADD_TWO(12,34));END;

Which procudes the output:

RESULT IS: 46

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Dropping Functions

To drop a function, you do it in a similar way to a procedure.

You simply say:

DROP FUNCTION function_name;

CREATE OR REPLACE PROCEDURE Find(mini OUT NUMBER,maxi OUT NUMBER) ISBEGINSELECT MAX(rating ),MIN(rating ) INTO maxi,mini FROM sailors;END Find;/

DECLAREmaxi NUMBER;mini NUMBER;BEGINFind(mini,maxi);

DBMS_OUTPUT.PUT_LINE('MAXIMUM AND MINIMUM OF rating from sailor '||maxi||','||mini);

END;/

Q. write a procedure to find the minimum and maximum rating of

sailors from sailors table .Display this value in the main program.

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CREATE TABLE sailors( sid integer not null,

sname varchar(32),

rating integer,

age real,CONSTRAINT PK_sailors PRIMARY KEY (sid) );

INSERT INTO sailors

( sid, sname, rating, age )

VALUES ( 22, 'Dustin', 7, 45.0 )

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When we execute an SQL statement from PL/SQL the oracle RDBMS assigns

a private work area of for that statement. This work contains information

about the SQL statement and the set of data returned or affected by thatstatement. The PL/SQL cursor is a mechanism by which we can name that

work area and manipulate the information within it. In simply way cursor is

defined as a pointer into a table in the database

SyntaxCURSOR cursor name as select from table name;

CURSOR are classified into two;Implicit 2. Explicit.

Implicit cursor:When select INTO or any DML statement is issued then ORACLE internally

opens the cursor. It is named as sql.

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Explicit cursor:

When Queries return more than one row, then cursor has to be defined

explicitly. The cursor should be declared on declaration part of pl/sql block. You

use three commands to control a cursor: OPEN, FETCH, and CLOSE. First, youinitialize the cursor with the OPEN statement, which identifies the result set.

Then, you use the FETCH statement to retrieve the first row. You can execute

FETCH repeatedly until all rows have been retrieved. When the last row has been

processed, you release the cursor with the CLOSE statement. We can process

several queries in parallel by declaring and opening multiple cursors.

Q.The HRD manager has decided to raise the salary for

all the employees in deptno 20 by 0.05

whenever any such raise is given to the employee

a record for that is maintained in the empraise

table it includes the empno,date.

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Write a PL/SQL block of code to update the salary of each

employee

and insert a record in the empraise table.create table employe(empcode varchar(10) primary

key,ename varchar(20),deptno number(5),job

varchar(20),salary number(8,2));

insert into employe

values('C101','vidhya',20,'clerk',5000);insert into employe

values('C102','maya',30,'teache',10000);insert into employe

values('C103','anjali',40,'teacher',15000);select * from employe;create table empraise(empcode varchar(10),raisedate date,

amount number(8,2));

d l

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declarecursor cemp is select empcode,salary from employe where

deptno=20;strempcode employe.empcode%type;numsalary employe.salary%type;beginopen cemp;loopfetch cemp into strempcode,numsalary;if cemp%found thenupdate employe set salary=numsalary+(numsalary*0.05)where empcode=strempcode;insert into empraise

values(strempcode,sysdate,numsalary*0.05);elseexit;end if;end loop;commit;close cemp;end;

/

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Q.Write a PL/SQL block that will display the name, department & salary of the firsttwo employees getting the highest salary

insert into employee values('anu',20,5250);insert into employee values('vidya',25,3000);insert into employee values('anjali',30,5500);insert into employee values('veena',35,2000);

create table employee(name varchar(10),dept number(8),

salary number(8));

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declareCursor C is select NAME,DEPT,SALARY from employee order

by salary;n varchar(10);s number(8);d number(8);beginopen c;dbms_output.put_line(' NAME DEPT SALARY');

loopfetch c into n,d,s;dbms_output.put_line(N||' '||D||' '||S);EXIT when c%rowcount=2;end loop;close c;

end;/

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CREATE OR REPLACE PROCEDURE FinddetailsIS

BEGINDECLARECURSOR s_sailors IS SELECT * FROM sailorsWHERE rating >7;

BEGINDBMS_OUTPUT.PUT_LINE('sid sname age');DBMS_OUTPUT.PUT_LINE('........ ..........

..........');for i IN s_sailorsloopDBMS_OUTPUT.PUT_LINE(i.sid||' '||i.sname||'

'||i.age);end loop;END;END Finddetails;

beginFinddetails;END;/

Q. Write a procedure(using cursor) to find the details of sailors whose rating greater

than 7