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Database Application
Development using
PL/SQL Programming
PL/SQL Programming
Chapter 1. Introduction
PL/SQL Programming
Introduction to PL/SQL
• PL/SQL is the procedural extension to SQL with
design features of programming languages.
• Data manipulation and query statements of SQL are
included within procedural units of code.
PL/SQL Programming
PL/SQL Environment
PL/SQL Engine
PL/SQL
block
PL/SQL
block
Procedural
Statement
executor
SQL statement
executor
Oracle server
PL/SQL Programming
PL/SQL and Oracle-based Applications
Oracle applications are designed for client-server architecture.
PL/SQL Programming
Programming in Oracle Applications
• Design and creation of database;
• Creation of database triggers;
• Building complex business rules at the database
level;
• Building screens, reports for user interface (Objects in
these applications may require PL/SQL codes)
PL/SQL Programming
Benefits:
 Integration
 Improved performance
 Modularised Program Development
 Portability
 Control Structures
 Error Handling
PL/SQL Programming
Chapter 2. Declaring Variables
PL/SQL Programming
Objectives
 Recognise the basic PL/SQL block and its sections
 Describe the significance of variables in PL/SQL
 Distinguish between PL/SQL and non-PL/SQL variables
 Declare PL/SQL variables
 Execute PL/SQL blocks
PL/SQL Programming
PL/SQL Block Structure
DECLARE (Optional)
constants
variables
cursors
user-defined exceptions
BEGIN (Mandatory)
SQL statements
PL/SQL statements
EXCEPTION (Optional)
Exception handling
END; (Mandatory)
PL/SQL Programming
PL/SQL Block Structure
• PL/SQL Block can have a
header that goes on top
of the block;
• The header specifies
whether the block is a
procedure, a function or
a package;
• If the header is absent,
the block is said to be an
anonymous block.
<Block Header>
DECLARE (Optional)
constants
variables
cursors
user-defined exceptions
BEGIN (Mandatory)
SQL statements
PL/SQL statements
EXCEPTION (Optional)
Exception handling
END; (Mandatory)
PL/SQL Programming
Executing Statements and PL/SQL Blocks
DECLARE
v_variable VARCHAR2(5);
BEGIN
SELECT column_name
INTO
v_variable
FROM
table_name;
EXCEPTION
WHEN exception_name THEN
...
END;
/
PL/SQL Programming
Block Types
Anonymous
Function
Procedure
[DECLARE]
PROCEDURE name
IS
BEGIN
-- statements
BEGIN
-- statements
[EXCEPTION]
[EXCEPTION]
FUNCTION name
RETURN datatype
IS
BEGIN
--statements
RETURN value;
[EXCEPTION]
END;
END;
END;
PL/SQL Programming
Program Constructs
 Anonymous blocks
 Stored procedures or functions
 Application procedures or functions
 Packages (Application or Stored)
 Database triggers (triggered by DML statements)
 Application triggers
PL/SQL Programming
Use of variables
Variables can be used for:




Temporary storage of data
Manipulation of stored values
Reusability
Ease of maintenance
PL/SQL Programming
Handling variables in PL/SQL
 Declare and initialise variables within the declarative
section
 Assign new values to variables within the executable
section
 Pass values into PL/SQL blocks through parameters
 View results through output variables
PL/SQL Programming
Types of variables
PL/SQL variables




Scalar
Composite
Reference
LOB (Large objects)
Non-PL/SQL variables
 Bind and host variables
PL/SQL Programming
Examples

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
TRUE
30-MAY-78
photo
text of a speech
8523.25
Movie
“Dhaka”
represents a Boolean value.
represents a DATE.
represents a LOB.
represents a LONG.
represents a NUMBER.
represents a BFILE.
represents a VARCHAR2.
PL/SQL Programming
Declaring PL/SQL Variables
Syntax:
identifier [CONSTANT] datatype [NOT NULL]
[:= | DEFAULT expr];
Examples:
v_hire_date
v_department_id
v_city
c_commission_pct
DATE;
NUMBER(4) NOT NULL := 10;
VARCHAR2(30) := ‘Sylhet’;
CONSTANT NUMBER := 1400;
PL/SQL Programming
Guidelines for Declaring PL/SQL Variables
• Follow a naming convention.
• Initialise variables designated as NOT NULL and
CONSTANT.
• Declare one identifier per line.
• Initialise identifiers by using the assignment operator (:=)
or the DEFAULT reserved word.
identifier := expr;
PL/SQL Programming
Naming Rules
•
•
•
Two variables can have the same name, provided
they are in different blocks.
The variable name should not be the same as the
name of columns of the table(s) used in the block.
Adopt a naming convention for identifiers.
For example: v_variable for a variable;
c_constant for a constant;
g_message for a global (or host) variable;
•
An identifier must not be longer than 30 characters.
PL/SQL Programming
Naming Rules
DECLARE
employee_id NUMBER(6);
BEGIN
SELECT employee_id
Better
INTO employee_id
FROM employees
WHERE last_name = ‘Smith’;
END;
to avoid
PL/SQL Programming
Variable Initialization and Keywords
• Assignment operator (:=)
• DEFAULT keyword
• NOT NULL constraint
Syntax:
identifier := expr;
Examples:
v_hiredate := ’31-DEC-98’ ;
v_mgr NUMBER(6) DEFAULT 100;
v_name := ‘King’;
PL/SQL Programming
Scalar Data Types
• Hold a single value
• Have no internal components
• Classified into four categories (they may have sub-types)
-> number
-> character
-> date
-> boolean
PL/SQL Programming
Base Scalar Data Types
•
•
•
•
•
•
•
•
CHAR [(maximum_length)]
VARCHAR2 [(maximum_length)]
LONG
LONG RAW
NUMBER [(precision, scale)]
BINARY_INTEGER
PLS_INTEGER
BOOLEAN
PL/SQL Programming
Base Scalar Data Types
•
•
•
•
•
•
DATE
TIMESTAMP
TIMESTAMP WITH TIME ZONE
TIMESTAMP WITH LOCAL TIME ZONE
INTERVAL YEAR TO MONTH
INTERVAL DAY TO SECOND
PL/SQL Programming
Scalar Variable Declarations
DECLARE
v_job
v_count
v_total_sal
v_orderdate
c_tax_rate
v_valid
…
VARCHAR2 (9);
BINARY_INTEGER := 0;
NUMBER (9,2) := 0;
DATE := SYSDATE + 7;
CONSTANT NUMBER (3,2) := 8.25;
BOOLEAN NOT NULL := TRUE;
PL/SQL Programming
The %TYPE Attribute
• Declare a variable according to:
 A database column definition
 Another previously declared variable
• Prefix %TYPE with:
 The database table and column
 The previously declared variable name
PL/SQL Programming
Declaring Variables with the %TYPE Attribute
Syntax:
identifier Table.column_name%TYPE;
Examples:
…
v_name
employees.last_name%TYPE;
v_balance
NUMBER(7,2);
v_min_balance v_balance%TYPE := 10;
…
PL/SQL Programming
Declaring Boolean Variables
•
•
•
•
Only the values TRUE, FALSE, and NULL can be assigned to a
Boolean variable.
The variables are compared by the logical operators AND, OR, and
NOT.
The variables always yield TRUE, FALSE, or NULL.
Arithmetic, character, and date expressions can be used to return a
Boolean value.
v_sal1 := 50000;
v_sal2 := 60000;
v_sal1 < v_sal2
DECLARE
v_flag BOOLEAN := FALSE;
BEGIN
v_flag := TRUE;
END;
PL/SQL Programming
Composite Datatypes
• PL/SQL TABLES
• PL/SQL RECORDS
PL/SQL Programming
LOB Data Type Variables
CLOB (character large object)
– stores large blocks of single-byte character data (Book)
BLOB (binary large object)
– stores large binary objects (Photo)
BFILE (binary file)
– stores large binary objects in operating system files (Movie)
NCLOB (national language character large object)
– stores unicode data
PL/SQL Programming
Bind Variables
• A variable declared in a host environment.
• Used to pass run-time values (character or number)
How to create? In SQL*Plus environment VARIABLE
VARIABLE
return_code NUMBER
return_message VARCHAR2(30)
How to reference in PL/SQL Block?
Needs to be preceded by a colon.
:bind_variable
How to display?
PRINT bind_variable
PL/SQL Programming
Using Bind Variables
Example:
In SQL*Plus prompt, declareVARIABLE g_salary NUMBER
BEGIN
SELECT salary
INTO :g_salary
FROM employees
WHERE employee_id = 178;
END;
PL/SQL Programming
DBMS_OUTPUT.PUT_LINE
• Oracle-supplied packaged procedure
• An alternative for displaying data from a PL/SQL block
• Needs to be enabled with SET SERVEROUTPUT ON
SET SERVEROUTPUT ON
DEFINE p_annual_sal = 60000;
DECLARE
v_sal NUMBER(9,2) := &p_annual_sal;
BEGIN
v_sal := v_sal/12;
DBMS_OUTPUT.PUT_LINE (‘Monthly salary
is ‘ || TO_CHAR(v_sal));
END;
PL/SQL Programming
Time for
Practice 2