Introduction to PLSQL.PPT

PL/SQL : INTRODUCTION
Ms.Sujaya S
Assistant Professor
Department of CSE
KIT-Kalaignarkarunanidhi Institute of Technology

PL/SQL
• PL/SQL is Oracle's procedural language extension
to SQL, the non-procedural relational database
language.
• With PL/SQL, you can use SQL statements to
manipulate ORACLE data and the flow of control
statements to process the data. Moreover, you can
declare constants and variables, define
subprograms (procedures and functions), and trap
runtime errors. Thus, PL/SQL combines the data
manipulating power of SQL with the data
processing power of procedural languages.

PL/SQL
• Many Oracle applications are built using client-server
architecture. The Oracle database resides on the server.
• The program that makes requests against this database
resides on the client machine.
• This program can be written in C, Java, or PL/SQL.
• While PL/SQL is just like any other programming
language, it has syntax and rules that determine how
programming statements work together. It is important
for you to realize that PL/SQL is not a stand-alone
programming language.
• PL/SQL is a part of the Oracle RDBMS, and it can reside
in two environments, the client and the server.

PL/SQL
• As a result, it is very easy to move PL/SQL
modules between server-side and client-side
applications.
• When the PL/SQL engine is located on the
server, the whole PL/SQL block is passed to the
PL/SQL engine on the Oracle server.
• The PL/SQL engine processes the block
according to the Figure 2.1.

PL/SQL
• When the PL/SQL engine is located on the client,
as it is in the Oracle Developer Tools, the
PL/SQL processing is done on the client side.
• All SQL statements that are embedded within
the PL/SQL block are sent to the Oracle server
for further processing. When PL/SQL block
contains no SQL statement, the entire block is
executed on the client side.

DIFFERENCE BETWEEN PL/SQL AND SQL
• When a SQL statement is issued on the client
computer, the request is made to the database on
the server, and the result set is sent back to the
client.
• As a result, a single SQL statement causes two trips
on the network. If multiple SELECT statements are
issued, the network traffic increase significantly very
fast. For example, four SELECT statements cause
eight network trips.
• If these statements are part of the PL/SQL block, they
are sent to the server as a single unit. The SQL
statements in this PL/SQL program are executed at
the server and the result set is sent back as a single
unit. There is still only one network trip made as is in
case of a single SELECT statement.

Comparison of SQL*PLUS and PL/SQL

PL/SQL BLOCKS
• PL/SQL blocks can be divided into two groups:
1. Named and
2. Anonymous.
• Named blocks are used when creating subroutines.
These subroutines are procedures, functions, and
packages.
• The subroutines can be stored in the database and
referenced by their names later on.
• In addition, subroutines can be defined within the
anonymous PL/SQL block.
• Anonymous PL/SQL blocks do not have names. As a
result,they cannot be stored in the database and
referenced later.

PL/SQL BLOCK STRUCTURE
• PL/SQL blocks contain three sections
1. Declare section
2. Executable section and
3. Exception-handling section.
• The executable section is the only mandatory
section of the block.
• Both the declaration and exception-handling
sections are optional.

PL/SQL BLOCK STRUCTURE
• PL/SQL block has the following structure:
DECLARE
Declaration statements
BEGIN
Executable statements
EXCETION
Exception-handling statements
END ;

DECLARATION SECTION
• The declaration section is the first section of
the PL/SQL block.
• It contains definitions of PL/SQL identifiers
such as variables, constants, cursors and so on.
• Example
DECLARE
v_first_name VARCHAR2(35) ;
v_last_name VARCHAR2(35) ;
v_counter NUMBER := 0 ;

EXECUTABLE SECTION
• The executable section is the next section of the
PL/SQL block.
• This section contains executable statements that allow
you to manipulate the variables that have been
declared in the declaration section.
BEGIN
SELECT first_name, last_name
INTO v_first_name, v_last_name
FROM student
WHERE student_id = 123 ;
DBMS_OUTPUT.PUT_LINE
(‘Student name :’ || v_first_name ||‘ ’|| v_last_name);
END;

EXCEPTION-HANDLING SECTION
• The exception-handling section is the last
section of the PL/SQL block.
• This section contains statements that are
executed when a runtime error occurs within a
block.
• Runtime errors occur while the program is
running and cannot be detected by the PL/SQL
compiler.
EXCEPTION
WHEN NO_DATA_FOUND THEN
(‘ There is no student with student id 123 ’);
END;

HOW PL/SQL GETS EXECUTED
• Every time an anonymous block is executed, the
code is sent to the PL/SQL engine on the server
where it is compiled.
• The named PL/SQL block is compiled only at the
time of its creation, or if it has been changed.
• The compilation process includes syntax checking,
binding and p-code generation.
• Syntax checking involves checking PL/SQL code for
syntax or compilation errors.
• Once the programmer corrects syntax errors, the
compiler can assign a storage address to program
variables that are used to hold data for Oracle. This
process is called Binding.

HOW PL/SQL GETS EXECUTED
• After binding, p-code is generated for the
PL/SQL block.
• P-code is a list of instructions to the PL/SQL
engine.
• For named blocks, p-code is stored in the
database, and it is used the next time the
program is executed.
• Once the process of compilation has completed
successfully, the status for a named PL/SQL
block is set to VALID, and also stored in the
database.
• If the compilation process was not successful,
the status for a named PL/SQL block is set to
INVALID.

PL/SQL IN SQL*PLUS
• SQL*Plus is an interactive tool that allows
you to type SQL or PL/SQL statements at
the command prompt.
• These statements are then sent to the
database. Once they are processed, the
results are sent back from the database
and displayed on the screen.
• There are some differences between
entering SQL and PL/SQL statements.

SQL EXAMPLE
FROM student;
• The semicolon terminates this SELECT
statement. Therefore, as soon as you type
semicolon and hit the ENTER key, the
result set is displayed to you.

PL/SQL EXAMPLE
DECLARE
v_first_name VARCHAR2(35);
v_last_name VARCHAR2(35);
BEGIN
FROM student
WHERE student_id = 123;
('Student name: '||v_first_name||' '||v_last_name);
EXCEPTION
('There is no student with student id 123');
END;
.
/

PL/SQL EXAMPLE
• There are two additional lines at the end of the
block containing “.” and “/”. The “.” marks the end of
the PL/SQL block and is optional.
• The “/” executes the PL/SQL block and is required.
• When SQL*Plus reads SQL statement, it knows that
the semicolon marks the end of the statement.
Therefore, the statement is complete and can be
sent to the database.
• When SQL*Plus reads a PL/SQL block, a semicolon
• marks the end of the individual statement within
the block. In other words, it is not a block
terminator.

PL/SQL EXAMPLE
• Therefore, SQL*Plus needs to know when the
block has ended. As you have seen in the
example, it can be done with period and
forward slash.

EXECUTING PL/SQL
PL/SQL can be executed directly in SQL*Plus.
A PL/SQL program is normally saved with
an .sql extension. To execute an
anonymous PL/SQL program, simply type
the following command at the SQL
prompt:
SQL> @DisplayAge

GENERATING OUTPUT
Like other programming languages, PL/SQL provides a
procedure (i.e. PUT_LINE) to allow the user to
display the output on the screen. For a user to able
to view a result on the screen, two steps are
required.
First, before executing any PL/SQL program, type the
following command at the SQL prompt (Note: you
need to type in this command only once for every
SQL*PLUS session):
SQL> SET SERVEROUTPUT ON;
or put the command at the beginning of the program,
right before the declaration section.

GENERATING OUTPUT
Second, use DBMS_OUTPUT.PUT_LINE in your
executable section to display any message you
want to the screen.
Syntax for displaying a message:
DBMS_OUTPUT.PUT_LINE(<string>);
in which PUT_LINE is the procedure to generate the
output on the screen, and DBMS_OUTPUT is the
package to which the PUT_LINE belongs.
DBMS_OUTPUT_PUT_LINE(‘My age is ‘ ||
num_age);

SUBSTITUTIONVARIABLES
• SQL*Plus allows a PL/SQL block to receive input
information with the help of substitution
variables.
• Substitution variables cannot be used to output
the values because no memory is allocated for
them.
• SQL*Plus will substitute a variable before the
PL/SQL block is sent to the database.
• Substitution variables are usually prefixed by the
ampersand(&) character or double ampersand
(&&) character.

EXAMPLE
DECLARE
v_student_id NUMBER := &sv_student_id;
v_first_name VARCHAR2(35);
v_last_name VARCHAR2(35);
BEGIN
FROM student
WHERE student_id = v_student_id;
('Student name: '||v_first_name||' '||v_last_name);
EXCEPTION
DBMS_OUTPUT.PUT_LINE('There is no such student');
END;

EXAMPLE
• When this example is executed, the user is asked
to provide a value for the student ID.
• The example shown above uses a single
ampersand for the substitution variable.
• When a single ampersand is used throughout
the PL/SQL block, the user is asked to provide a
value for each occurrence of the substitution
variable.

EXAMPLE
BEGIN
DBMS_OUTPUT.PUT_LINE('Today is ‘||’&sv_day');
DBMS_OUTPUT.PUT_LINE('Tomorrow will be ‘||’ &sv_day');
END;
This example produces the following output:
Enter value for sv_day: Monday
old 2: DBMS_OUTPUT.PUT_LINE('Today is ‘||’ &sv_day');
new 2: DBMS_OUTPUT.PUT_LINE('Today is ‘||’ Monday');
Enter value for sv_day: Tuesday
old 3: DBMS_OUTPUT.PUT_LINE('Tomorrow will be ‘||’ &sv_day');
new 3: DBMS_OUTPUT.PUT_LINE('Tomorrow will be ‘||’ Tuesday');
Today is Monday
Tomorrow will be Tuesday
PL/SQL procedure successfully completed.

EXAMPLE
• When a substitution variable is used in the
script, the output produced by the program
contains the statements that show how the
substitution was done.
• If you do not want to see these lines displayed
in the output produced by the script, use the
SET command option before you run the script
as shown below:
SET VERIFY OFF;

EXAMPLE
• Then, the output changes as shown below:
Enter value for sv_day: Tuesday
Today is Monday
Tomorrow will be Tuesday
• The substitution variable sv_day appears twice in this PL/SQL block. As a
result, when this example is run, the user is asked twice to provide the value
for the same variable.

EXAMPLE
BEGIN
DBMS_OUTPUT.PUT_LINE('Today is '||'&&sv_day');
DBMS_OUTPUT.PUT_LINE('Tomorrow will be ‘||’ &sv_day');
END;
• In this example, substitution variable sv_day is
prefixed by double ampersand in the first
DBMS_OUTPUT.PUT_LINE statement. As a result,
this version of the example produces different
output.

OUTPUT
old 2: DBMS_OUTPUT.PUT_LINE('Today is ‘||’ &&sv_day');
new 2: DBMS_OUTPUT.PUT_LINE('Today is ‘||’ Monday');
old 3: DBMS_OUTPUT.PUT_LINE('Tomorrow will be ‘||’ &sv_day');
new 3: DBMS_OUTPUT.PUT_LINE('Tomorrow will be ‘||’ Monday');
Today is Monday
Tomorrow will be Monday
• It is clear that the user is asked only once to provide the value for
the substitution variable sv_day.
• As a result, both DBMS_OUTPUT.PUT_LINE statements use the
value of Monday entered previously by the user.

Substitution Variables
 Ampersand(&) character and double ampersand
(&&) characters are the default characters that
denote substitution variables.
 There is a special SET command option available in
SQL*Plus that allows to change the default character
(&) to any other character or disable the substitution
variable feature.
 This SET command has the following syntax:
SET DEFINE character
or
SET DEFINE ON
or
SET DEFINE OFF

Substitution Variables
 The first set command option changes the prefix
of the substitution variable from an ampersand
to another character. This character cannot be
alphanumeric or white space.
 The second (ON option) and third (OFF option)
control whether SQL*Plus will look for
substitution variables or not.
 In addition, ON option changes the value of the
character back to the ampersand.

Introduction to PLSQL.PPT

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