oracle slides02 fp2005 ver 1.0

PL/SQL
Oracle Day 2
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Objectives
•
To explain the need for a procedural language and the constructs
of PL/SQL.
•
To explain Exception/Error handling in PL/SQL blocks such as
Named and Un-named System Exceptions, User defined
Exceptions
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About 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.
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PL/SQL
block
PL/SQL engine
Oracle server
Procedural
statement
executor
PL/SQL
SQL
SQL statement executor
PL/SQL
block
PL/SQL Environment
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Application
Oracle server
Shared
library
Integration
Benefits of PL/SQL 1/4
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Application
Other DBMSs
Application
Oracle with
PL/SQL
SQL
SQL
SQL
SQL
SQL
IF THEN
SQL
ELSE
SQL
END IF;
SQL
Improved performance
Benefits of PL/SQL 2/4
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DECLARE

BEGIN
END;
EXCEPTION
Benefits of PL/SQL 3/4
Modularize program development
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•
PL/SQL is portable
•
You can declare variables
•
You can program with procedural language control
structures.
•
PL/SQL can handle errors.

Benefits of PL/SQL 4/4
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DECLARE (Optional)
Variables, cursors, user-defined exceptions

BEGIN (Mandatory)
–
SQL statements
–
PL/SQL statements
EXCEPTION (Optional)
Actions to perform when errors occur
END; (Mandatory)
END;
PL/SQL Block Structure
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DECLARE
var1 VARCHAR2(5);
BEGIN
SELECT column_name
INTO var1
FROM t1;
EXCEPTION
WHEN exception THEN

END;
Executing Statements and PL/SQL Blocks
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Anonymous Procedure Function
[DECLARE]
BEGIN
statements
[EXCEPTION]
END;
PROCEDURE name
IS
BEGIN
statements
[EXCEPTION]
END;
FUNCTION name
RETURN datatype
IS
BEGIN
statements
RETURN value;
[EXCEPTION]
END;
Block Types
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Variables can be used for:
•
Temporary storage of data
•
Manipulation of stored values
•
Reusability
•
Ease of maintenance
Use of Variables
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
Declare and initialize variables in the declaration
section.

Assign new values to variables in the executable
section.

Pass values into PL/SQL blocks through parameters.

View results through output variables.
Handling Variables in PL/SQL
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•
PL/SQL variables:
–
Scalar
–
Composite
–
Reference
–
LOB (large objects)
•
Non-PL/SQL variables: Bind and host variables
Types of Variables
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identifier [CONSTANT] datatype [NOT NULL]
[:= | DEFAULT expr];
DECLARE
v_date DATE;
v_dno NUMBER(2) NOT NULL := 5;
v_location VARCHAR2(13) := ‘Berhampur’;
c_incentive CONSTANT NUMBER := 100;
Syntax:

Examples:
Declaring PL/SQL Variables
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identifier := expression;
Guidelines for Declaring PL/SQL Variables
•
Follow naming conventions.
•
Initialize variables designated as NOT NULL and
CONSTANT.
•
Declare one identifier per line.
•
Initialize identifiers by using the assignment operator (:=)
or the DEFAULT reserved word.
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DECLARE
empno NUMBER(6);
BEGIN
SELECT empno

INTO empno
FROM emp
WHERE ename = ‘Sanjukta';
END;
/
Follow a naming
convention for
PL/SQL identifiers:
e.g.: v_empno
•
Two variables can have the same name, provided they are in different
blocks.
•
The variable name (identifier) should not be the same as the name of
table columns used in the block.
Naming Rules
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identifier := expression;
v_joindate := '01-JAN-2004';
v_name := ‘Swetalina';
•
Assignment operator (:=)
•
DEFAULT keyword
•

NOT NULL constraint
Syntax:
Examples:
Variable Initialization and Keywords
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Scalar Data Types
•
CHAR [(maximum_length)]
•
VARCHAR2 (maximum_length)
•
LONG
•
LONG RAW
•
NUMBER [(precision, scale)]
•
BINARY_INTEGER
•
PLS_INTEGER
•
BOOLEAN
•
DATE
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DECLARE
v_name VARCHAR2(9);
v_count BINARY_INTEGER := 0;
v_sal NUMBER(9,2) := 0;
v_shipdate DATE := SYSDATE + 14;
c_tax CONSTANT NUMBER(3,2) := 6.75;
v_isMale BOOLEAN NOT NULL := TRUE;

Examples:
Scalar Variable Declarations
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•
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
The %TYPE Attribute
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v_name empl.name%TYPE;
v_bal NUMBER(7,2);
v_min_bal v_bal%TYPE := 10;

identifier Table.column_name%TYPE;
Declaring Variables
with the %TYPE Attribute
Examples:
Syntax:
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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.
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BFILE
BLOB
CLOB
LOB Data Type Variables
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Server
Bind variable
Bind Variables