PL/SQL Tutorial (Examples) - page 3
PL/SQL BLOCK
The pl/sql block contains the following section:--
-----The DECLARE section.
-----The Master BEGIN and END section that contains the EXCEPTION section.
The declare section contains declaration of memory variables, constants, cursors etc. The begin section contains sql executable statements and pl/sql executable
statements. The exception section contains code to handle errors that may arise during the execution of the code block. The end declares the end of pl/sql block.
A bit about it's working. When you typed out the pl/sql block for execution. It is sent to the pl/sql engine, where procedural statements are executed; and sql
statements are sent to the sql executor in the oracle engine. Since pl/sql engine resides in the oracle engine, the codes executes smoothly and efficiently.
PL/SQL DATA-TYPE
This is easy since it includes almost all the data types which u have used in
sql such as date, varchar, number, char etc etc... Some of the attributes such
as %TYPE is also used. This attribute automatically takes in the default data
type of the sql table from which u have passed the query. We will discuss this later.
Remember in pl/sql a variable name must begin with a character and can be
followed by maximum of 29 other characters. Reserved words can't be used unless
enclosed within double quotes. Variables must be separated from each other by at
least one space or by a punctuation mark. You can assign values of operator
using := operator. I won't discuss about logical comparisons operators such as
<, > , >=, NOT, TRUE, AND, OR, NULL etc since they r quite easy to understand.
HOW TO DISPLAY MESSAGES ON SCREEN ---
DBMS_OUTPUT : is a package that includes a number of procedure and functions that accumulate information in a buffer so that it can be retrieved later. These functions can also be used to display messages to the user.
PUT_LINE : Put a piece of information in the package buffer followed by an end-of-line marker. It can also be used to display message to the user. Put_line expects a single parameter of character data type. If used to display a message, it is the message 'string'.
EG: dbms_output.put_line(x);
REMEMBER: To display messages to the user the SERVEROUTPUT should be set to ON. SERVEROUTPUT is a sql*plus environment parameter that displays the information pased as a parameter to the PUT_LINE function.
EG: SET SERVEROUTPUT ON
A bit about comments. A comment can have 2 forms i.e.
-- The comment line begins with a double hyphen (--). The entire line will be treated as a comment.
-- The C style comment such as /* i am a comment */
CONDITIONAL CONTROL AND ITERATIVE CONTROL AND SEQUENTIAL CONTROL
IF and else.....
IF --Condition THEN
--Action
ELSEIF --Condition THEN
--Action
ELSE
--Action
END IF;
SIMPLE LOOP
loop
-- Sequence of statements;
end loop;
the loop ends when u use EXIT WHEN statement --condition
WHILE LOOP
While --condition
loop
--sequence of statements
end loop;
FOR LOOP
FOR i in 1..10
loop
--sequence of statements
end loop;
GOTO (sequential control)
GOTO X;
<< X >>
EXAMPLES
--ADDITION
declare
a number;
b number;
c number;
begin
a:=&a;
b:=&b;
c:=a+b;
dbms_output.put_line('Sum of ' || a || ' and ' || b || ' is ' || c);
Here & is used to take user input at runtime.....
--SUM OF 100 NUMBERS
Declare
a number;
s1 number default 0;
Begin
a:=1;
loop
s1:=s1+a;
exit when (a=100);
a:=a+1;
end loop;
dbms_output.put_line('Sum between 1 to 100 is '||s1);
End;
--SUM OF odd NUMBERS USING USER INPUT...for loop
declare
n number;
sum1 number default 0;
endvalue number;
begin
endvalue:=&endvalue;
n:=1;
for n in 1.. endvalue
loop
if mod(n,2)=1
then
sum1:=sum1+n;
end if
end loop;
dbms_output.put_line('sum = ' || sum1);
end;
--SUM OF 100 ODD NUMBER .. WHILE LOOP
declare
n number;
endvalue number;
sum1 number default 0;
begin
endvalue:=&endvalue;
n:=1;
while (n < endvalue)
loop
sum1:=sum1+n;
n:=n+2;
end loop;
dbms_output.put_line('Sum of odd numbers between 1 and ' || endvalue || ' is ' || sum1);
end;
--CALCULATION OF NET SALARY
declare
ename varchar2(15);
basic number;
da number;
hra number;
pf number;
netsalary number;
begin
ename:=&ename;
basic:=&basic;
da:=basic * (41/100);
hra:=basic * (15/100);
if (basic < 3000)
then
pf:=basic * (5/100);
elsif (basic >= 3000 and basic <= 5000)
then
pf:=basic * (7/100);
elsif (basic >= 5000 and basic <= 8000)
then
pf:=basic * (8/100);
else
pf:=basic * (10/100);
end if;
netsalary:=basic + da + hra -pf;
dbms_output.put_line('Employee name : ' || ename);
dbms_output.put_line('Providend Fund : ' || pf);
dbms_output.put_line('Net salary : ' || netsalary);
end;
--MAXIMUM OF 3 NUMBERS
Declare
a number;
b number;
c number;
d number;
Begin
dbms_output.put_line('Enter a:');
a:=&a;
dbms_output.put_line('Enter b:');
b:=&b;
dbms_output.put_line('Enter c:');
c:=&b;
if (a>b) and (a>c) then
dbms_output.putline('A is Maximum');
elsif (b>a) and (b>c) then
dbms_output.putline('B is Maximum');
else
dbms_output.putline('C is Maximum');
end if;
End;
--QUERY EXAMPLE--IS SMITH EARNING ENOUGH
declare
s1 emp.sal %type;
begin
select sal into s1 from emp
where ename = 'SMITH';
if(no_data_found)
then
raise_application_error
(20001,'smith is not present');
end if;
if(s1 > 10000)
then
raise_application_error
(20002,'smith is earning enough');
end if;
update emp set sal=sal + 500
where ename='SMITH';
end;
--PRIME NO OR NOT
DECLARE
no NUMBER (3) := &no;
a NUMBER (4);
b NUMBER (2);
BEGIN
FOR i IN 2..no - 1
LOOP
a := no MOD i;
IF a = 0
THEN
GOTO out;
END IF;
END LOOP;
<>
IF a = 1
THEN
DBMS_OUTPUT.PUT_LINE (no || ' is a prime number');
ELSE
DBMS_OUTPUT.PUT_LINE (no || ' is not a prime number');
END IF;
END;
--SIMPLE EXAMPLE OF LOOP STATEMENT I.E. EXIT WHEN
Declare
a number:= 100;
begin
loop
a := a+25;
exit when a=250;
end loop;
dbms_output.put_line (to_Char(a));
end;
--EXAMPLE OF WHILE LOOP
Declare
i number:=0;
j number:= 0;
begin
while i <=100 loop
j := j+1;
i := i +2;
end loop;
dbms_output.put_line(to_char(i));
end;
--EXAMPLE OF FOR LOOP
Declare
begin
for i in 1..10
loop
dbms_output.put_line(to_char(i));
end loop;
end;
--SEQUENTIAL CONTROL GOTO
declare
--takes the default datatype of the column of the table price
cost price.minprice%type;
begin
select stdprice into cost from price where prodial in (Select prodid from product where prodese = "shampoo");
if cost > 7000 then
goto Upd;
end if;
<< Upd >>
Update price set minprice = 6999 where prodid=111;
end;
--CALCULATE THE AREA OF A CIRCLE FOR A VALUE OF RADIUS VARYING FROM 3 TO 7. STORE THE RADIUS AND THE CORRESPONDING VALUES OF CALCULATED AREA IN A TABLE AREAS.
Declare
pi constant number(4,2) := 3.14;
radius number(5);
area number(14,2);
Begin
radius := 3;
While radius <=7
Loop
area := pi* power(radius,2);
Insert into areas values (radius, area);
radius:= radius+1;
end loop;
end;
--REVERSING A NUMBER 5639 TO 9365
Declare
given_number varchar(5) := '5639';
str_length number(2);
inverted_number varchar(5);
Begin
str_length := length(given_number);
For cntr in reverse 1..str_length
loop
inverted_number := inverted_number || substr(given_number, cntr, 1);
end loop;
dbms_output.put_line('The Given no is ' || given_number);
dbms_output.put_line('The inverted number is ' || inverted_number);
end;
EXCEPTION HANDLING IN PLSQL
Errors in pl/sql block can be handled...error handling refers to the way we handle the errors in pl/sql block so that no crashing stuff of code takes place...This is
exactly the same as we do in C++ or java..right!!
There are two type:
===> predefined exceptions
===> user defined exceptions
The above 2 terms are self explanatory
predefined exceptions:
No-data-found == when no rows are returned
Cursor-already-open == when a cursor is opened in advance
Dup-val-On-index == for duplicate entry of index..
Storage-error == if memory is damaged
Program-error == internal problem in pl/sql
Zero-divide == divide by zero
invalid-cursor == if a cursor is not open and u r trying to close it
Login-denied == invalid user name or password
Invalid-number == if u r inserting a string datatype for a number datatype which is already declared
Too-many-rows == if more rows r returned by select statement
SYNTAX
begin
sequence of statements;
exception
when --exception name then
sequence of statements;
end;
EXAMPLES
--When there is no data returned by row
declare
price item.actualprice%type;
begin
Select actual price into price from item where qty=888;
when no-data-found then
dbms_output.put_line('item missing');
end;
--EXAMPLE OF USER DEFINED EXCEPTION
DECLARE
e_rec emp%ROWTYPE;
e1 EXCEPTION;
sal1 emp.sal%TYPE;
BEGIN
SELECT sal INTO sal1 FROM emp WHERE deptno = 30 AND ename = 'John';
IF sal1 < 5000 THEN
RAISE e1;
sal1 := 8500;
UPDATE emp SET sal = sal1 WHERE deptno = 30 AND ename = 'John';
END IF;
EXCEPTION
WHEN no_data_found THEN
RAISE_APPLICATION_ERROR (-20001, 'John is not there.');
WHEN e1 THEN
RAISE_APPLICATION_ERROR (-20002, 'Less Salary.');
END;
--EXAMPLE OF RAISE-APPLICATION-ERROR... THIS IS YOUR OWN ERROR STATEMENT...YOU RAISE YOUR OWN ERROR
Declare
s1 emp.sal %type;
begin
select sal into s1 from emp where ename='SOMDUTT';
if(no-data-found) then
raise_application_error(20001, 'somdutt is not there');
end if;
if(s1 > 10000) then
raise_application_error(20002, 'somdutt is earing a lot');
end if;
update emp set sal=sal+500 where ename='SOMDUTT';
end;
--INTERESTING EG OF USER DEFINED EXCEPTIONS
Declare
zero-price exception;
price number(8);
begin
select actualprice into price from item where ordid =400;
if price=0 or price is null then
raise zero-price;
end if;
exception
when zero-price then
dbms_output.put_line('raised xero-price exception');
end;