Plsql overview

PL/SQL - Overview

Gagan Deep
Assistant Professor
University College,
Kurukshetra University, Kurukshetra

What is PL/SQL ?

• Procedural Language – SQL
• An extension to SQL with design features of
programming languages (procedural and object
oriented)
• PL/SQL and Java are both supported as internal
host languages within Oracle products.
Gagan Deep, Assistant Professor, UCK and Director, Rozy Computech Services, 3 rd Gate, K.U., Kurukshetra

PL/SQL
The PL/SQL procedural
language was developed by
Oracle Corporation in the late
1980s as procedural extension
language for SQL and the Oracle relational database.
Following are notable facts about PL/SQL:
•PL/SQL is a completely portable, high-performance
transaction-processing language.
•PL/SQL provides a built-in interpreted and OS
independent programming environment.

• PL/SQL can also directly be
called from the command-
line SQL*Plus interface.
• Direct call can also be made
from external programming
language calls to database.
• PL/SQL's general syntax is based on that of ADA
and Pascal programming language.
• Apart from Oracle, PL/SQL is available in
TimesTen in-memory database and IBM DB2.


Why PL/SQL
• Acts as host language for
stored procedures and triggers.
• Provides the ability to add
middle tier business logic to
client/server applications.
• Provides Portability of code from one
environment to another
• Improves performance of multi-query
transactions.
• Provides error handling

Features of PL/SQL
PL/SQL has the following features:
• PL/SQL is tightly integrated with
SQL.
• It offers extensive error checking.
• It offers numerous data types.
• It offers a variety of programming structures.
• It supports structured programming through functions
and procedures.
• It supports object oriented programming.
• It supports developing web applications and server
pages.

Advantages of PL/SQL
PL/SQL has the following
advantages :
•SQL is the standard database
language and PL/SQL is
strongly integrated with SQL. PL/SQL supports
both static and dynamic SQL.
• Static SQL supports DML operations and
transaction control from PL/SQL block.
• Dynamic SQL is SQL allows embedding DDL
statements in PL/SQL blocks.

• PL/SQL allows sending an
entire block of statements to the
database at one time. This
reduces network traffic and
provides high performance for
the applications.
• PL/SQL give high productivity to programmers as
it can query, transform, and update data in a
database.
• PL/SQL saves time on design and debugging by
strong features, such as exception handling,
encapsulation, data hiding, and object-oriented.

• Applications written in
PL/SQL are fully portable.
• PL/SQL provides high
security level.
• PL/SQL provides access to
predefined SQL packages.
• PL/SQL provides support for Object-Oriented
Programming.
• PL/SQL provides support for Developing Web
Applications and Server Pages.


Client-Server Architecture
• PL/SQL is a part of the Oracle RDBMS, and it can reside
in two environments, the client and the server.
• Many Oracle applications are built using client-server
architecture.
The Oracle database resides on the server.
• The program(` C, Java, or PL/SQL) that makes requests
against this database resides on the client machine.
• 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 1.

Figure 1 : The PL/SQL Engine and
Oracle Server

• 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.

Comparison of 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 PL/SQL
and SQL
Figure 2 : The PL/SQL in client –
server architecture

PL/SQL Block-Structure
PL/SQL is a block-structured
language, meaning that PL/SQL
programs are divided and written
in logical blocks of code. Each
block consists of three sub-parts:
1 Declarations :
This section starts with the keyword DECLARE.
It is an optional section and defines all
variables, cursors, subprograms, and other
elements to be used in the program.

2 Executable Commands
This section is enclosed between
the keywords BEGIN and
END and it is a mandatory
section. It consists of the
executable PL/SQL statements
of the program. It should have
at least one executable line of
code, which may be just a
NULL command to indicate
that nothing should be
executed.

3 Exception Handling
This section starts with the
keyword EXCEPTION.
This section is again optional
and contains exception(s)
that handle errors in the
program.

Every PL/SQL statement end with a semicolon
(;).
PL/SQL blocks can be nested within other
PL/SQL blocks using BEGIN and END.

PL/SQL Block Structure
DECLARE (optional)
- variable declarations
BEGIN (mandatory)
- SQL statements
- PL/SQL statements or sub-
blocks
EXCEPTION (optional)
- actions to perform when errors
occur
END; (mandatory)

PL/SQL Block Types

Function
Anonymous Procedure FUNCTION <name>
RETURN <datatype>
DECLARE PROCEDURE <name>
IS
BEGIN IS
BEGIN
-statements BEGIN
-statements
EXCEPTION -statements
EXCEPTION
END; EXCEPTION
END;
END;

Example
The end; line
signals the end of
the PL/SQL block.
DECLARE
message varchar2(20):= 'Hello, World!'; To run the code
BEGIN from SQL command
dbms_output.put_line(message); line, you may need
END; to type / at the
/ beginning of the
Hello, World ! first blank line after
PL/SQL procedure successfully the last line of the
completed.
code.

The PL/SQL Identifiers
• PL/SQL identifiers are constants,
variables, exceptions, procedures,
cursors, and reserved words. The
identifiers consist of a letter
optionally followed by more,
letters numerals, dollar signs, underscores, and
number signs and should not exceed 30 characters.
•By default, identifiers are not case-sensitive. So
you can use integer or INTEGER to represent a
numeric value. You cannot use a reserved keyword as
an identifier.

The PL/SQL Delimiters
A delimiter is a symbol with a special
meaning. Following is the list of
delimiters in PL/SQL:
Delimiter Description
Addition, subtraction/negation,
+, -, *, / multiplication, division

% Attribute indicator

' Character string delimiter

. Component selector

(,) Expression or list delimiter

Similarly, there are : Host variable indicator

more delimiters. , Item separator

The PL/SQL Comments
• Program comments are explanatory statements that you
can include in the PL/SQL code that you write and
helps anyone reading it's source code. All
programming languages allow for some form of
comments.
• The PL/SQL supports single line and multi-line
comments. All characters available inside any
comment are ignored by PL/SQL compiler. The
PL/SQL single-line comments start with the delimiter
-- (double hyphen) and multi-line comments are
enclosed by /* and */.

DECLARE
-- variable declaration
message varchar2(20):= 'Hello,
World!’;
BEGIN
/*
PL/SQL executable statement(s)
Example */
dbms_output.put_line(message);
END;
/
After Execution in SQL the result is : Hello, World!
PL/SQL procedure successfully completed.

Data Types
PL/SQL variables, constants and parameters must have
a valid data types which specifies a storage format,
constraints, and valid range of values. PL/SQL is
strongly typed. The following is the list of data types:
Category Description
Single values with no internal components,
Scalar such as a NUMBER, DATE, or BOOLEAN.
Pointers to large objects that are stored
separately from other data items, such as
Large Object (LOB) text, graphic images, video clips, and sound
waveforms.
Data items that have internal components
Composite that can be accessed individually. For
example, collections and records.

Reference Pointers to other data items.

Scalar Data Types
• PL/SQL Scalar Data Types and
Subtypes come under the following
categories:
Date Type Description
Numeric values, on which arithmetic operations
Numeric are performed.
Alphanumeric values that represent single
Character characters or strings of characters.
Logical values, on which logical operations are
Boolean performed.

Datetime Dates and times.

PL/SQL Numeric Data
Types
Data Type Description
ANSI and IBM specific floating-point type
FLOAT with maximum precision of 126 binary digits
(approximately 38 decimal digits)
ANSI and IBM specific integer type with
INTEGER OR INT
maximum precision of 38 decimal digits
Floating-point type with maximum precision
REAL of 63 binary digits (approximately 18 decimal
digits)
Signed integer in range -2,147,483,648
PLS_INTEGER OR BINARY_INTEGER
through 2,147,483,647, represented in 32 bits
ANSI specific fixed-point type with
DEC(prec, scale)
maximum precision of 38 decimal digits.


Following is a valid declaration:
DECLARE
num1 INTEGER;
num2 REAL;
num3 DOUBLE PRECISION;
BEGIN
Example null;
END;
/
When the above code is compiled and executed, it
produces following result:
PL/SQL procedure successfully completed

Character Data Types

Data Type Description
CHAR Fixed-length character string with maximum size of 32,767 bytes

VARCHAR Variable-length character string with maximum size of 32,767
2 bytes

Variable-length binary or byte string with maximum size of
RAW 32,767 bytes, not interpreted by PL/SQL
Variable-length character string with maximum size of 32,760
LONG bytes
ROWID Physical row identifier, the address of a row in an ordinary table


PL/SQL Operators
An operator is a symbol that tells the
compiler to perform specific
mathematical or logical manipulations.
PL/SQL language is rich in built-in
operators and provides following type
of operators:
•Arithmetic operators
•Relational operators
•Comparison operators
•Logical operators
•String operators

Precedence of Operators

Operator Operation
** exponentiation
+, - identity, negation
*, / multiplication, division
+, -, || addition, subtraction, concat
=, <, >, <=, >=, IS NULL, LIKE, IN Comparison
NOT logical negation
AND conjunction
OR inclusion


Control Structures
• Programming languages provide
various control structures that
allow for more complicated
execution paths.
• Decision making structures require that the
programmer specify one or more conditions to be
evaluated or tested by the program, along with a
statement or statements to be executed if the
condition is determined to be true, and optionally,
other statements to be executed if the condition is
determined to be false.

PL/SQL Decisions
Making
PL/SQL language provides
following types of decision
making statements.
•IF-THEN Statement
•IF-THEN-ELSE Statement
•IF-THEN-ELSEIF Statement
•Nested IF Statement

Syntax for IF-THEN statement
IF condition THEN
S;
END IF;
Where condition is a Boolean or relational
condition and S is a simple or compound
statement.
Example of an IF-THEN statement is:
IF (a <= 20) THEN
c:= c+1;
END IF;

DECLARE Example
a number(2) := 10;
BEGIN
a:= 10;
IF( a < 20 ) THEN
dbms_output.put_line('a is less than 20' );
END IF;
dbms_output.put_line('value of a is:' || a);
END;
/ After Execution :
a is less than 20 value of a is : 10
PL/SQL procedure successfully completed.

PL/SQL - Loops
PL/SQL provides the following
types of loop to handle the looping
requirements

•BASIC LOOP
•WHILE LOOP
•FOR LOOP
•NESTED LOOP

Syntax of Basic Loop

The syntax of a basic loop in PL/SQL language
is:
LOOP
Sequence of statements;
END LOOP


Example
DECLARE
x number := 10;
BEGIN LOOP
dbms_output.put_line(x);
x := x + 10;
IF x > 50 THEN exit; END IF;
END LOOP;
dbms_output.put_line('After Exit x is: ' || x);
END;
/
After Execution is : 10 20 30 40 50 After Exit x is: 60

Syntax of For Loop
FOR counter IN i_value .. f_value LOOP
sequence_of_statements;
END LOOP;
Following are special characteristics of FOR loop:
The i_value and f_value of the loop variable or counter can
be literals, variables, or expressions but must evaluate to
numbers. Otherwise, PL/SQL raises the predefined
exception VALUE_ERROR.
The i_value need not to be 1; however, the loop counter
increment (or decrement) must be 1.
PL/SQL allows determine the loop range dynamically at
runGagan Deep, Assistant Professor, UCK and Director, Rozy Computech Services, 3 Gate, K.U., Kurukshetra
time. rd

Example
DECLARE
a number(2);
BEGIN
Result is
FOR a in 10 .. 15 LOOP
value of a: 10
dbms_output.put_line('value of a: ' ||
value of a: 11
a);
value of a: 12
END LOOP;
value of a: 13
END;
value of a: 14
/
value of a: 15

Common PL/SQL String
Functions
• CHR(ASCIIvalue)
• ASCII(string)
• LOWER(string)
• SUBSTR(string,start,substrlength)
• LTRIM(string)
• RTRIM(string)
• REPLACE(string, searchstring,
replacestring)
• UPPER(string)
Gagan Deep, Assistant Professor, UCK and
• INITCAP(string)
Director, Rozy Computech Services, 3
• LENGTH(string)
rd

Gate, K.U., Kurukshetra

Common PL/SQL Numeric
Functions

• ABS(value)
• ROUND(value, precision)
• MOD(value,divisor)
• SQRT(value)
• TRUNC(value,|precision|)
• LEAST(exp1, exp2…)
• GREATEST(exp1, exp2…

When is PL/SQL
handy
• When something is too
complicated for SQL
• When conditional branching
and looping are needed.


Thanks !
If you have any query please mail me at
rozygag@yahoo.com

Plsql overview

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