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Declaring PL/SQL Variables

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Objectives After completing this lesson, you should be able to do the following: Recognize valid and invalid identifiers List the uses of variables Declare and initialize variables List and describe various data types Identify the benefits of using the %TYPE attribute Declare, use, and print bind variables

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Use of Variables Variables can be used for: Temporary storage of data Manipulation of stored values Reusability

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Requirements for Variable Names A variable name: Must start with a letter Can include letters or numbers Can include special characters (such as $, _, and # ) Must contain no more than 30 characters Must not include reserved words

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Handling Variables in PL/SQL Variables are: Declared and initialized in the declarative section Used and assigned new values in the executable section Passed as parameters to PL/SQL subprograms Used to hold the output of a PL/SQL subprogram

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Declaring and Initializing PL/SQL Variables Syntax: Examples:

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Declaring and Initializing PL/SQL Variables

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Delimiters in String Literals

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Types of Variables PL/SQL variables: Scalar Composite Reference Large object (LOB) Non-PL/SQL variables: Bind variables

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Types of Variables

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Guidelines for Declaring and Initializing PL/SQL Variables Follow naming conventions. Use meaningful identifiers for variables. Initialize variables designated as NOT NULL and CONSTANT. Initialize variables with the assignment operator (:=) or the DEFAULT keyword: Declare one identifier per line for better readability and code maintenance.

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Guidelines for Declaring PL/SQL Variables Avoid using column names as identifiers. Use the NOT NULL constraint when the variable must hold a value.

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Scalar Data Types Hold a single value Have no internal components

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Base Scalar Data Types CHAR [(maximum_length)] VARCHAR2 (maximum_length) NUMBER [(precision, scale)] BINARY_INTEGER PLS_INTEGER BOOLEAN BINARY_FLOAT BINARY_DOUBLE

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Base Scalar Data Types DATE TIMESTAMP TIMESTAMP WITH TIME ZONE TIMESTAMP WITH LOCAL TIME ZONE INTERVAL YEAR TO MONTH INTERVAL DAY TO SECOND

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Declaring Scalar Variables Examples:

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%TYPE Attribute Is used to declare a variable according to: A database column definition Another declared variable Is prefixed with: The database table and column names The name of the declared variable

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Declaring Variables with the %TYPE Attribute Syntax Examples

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Declaring Boolean Variables Only the TRUE, FALSE, and NULL values can be assigned to a Boolean variable. Conditional expressions use the logical operators AND and OR and the unary operator NOT to check the variable values. 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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Bind Variables Bind variables are: Created in the environment Also called host variables Created with the VARIABLE keyword Used in SQL statements and PL/SQL blocks Accessed even after the PL/SQL block is executed Referenced with a preceding colon

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Printing Bind Variables Example:

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Printing Bind Variables Example:

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LOB Data Type Variables

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Composite Data Types

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Quiz The %TYPE attribute: Is used to declare a variable according to a database column definition Is used to declare a variable according to a collection of columns in a database table or view Is used to declare a variable according the definition of another declared variable Is prefixed with the database table and column names or the name of the declared variable

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Summary In this lesson, you should have learned how to: Recognize valid and invalid identifiers Declare variables in the declarative section of a PL/SQL block Initialize variables and use them in the executable section Differentiate between scalar and composite data types Use the %TYPE attribute Use bind variables

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Practice 2: Overview This practice covers the following topics: Determining valid identifiers Determining valid variable declarations Declaring variables within an anonymous block Using the %TYPE attribute to declare variables Declaring and printing a bind variable Executing a PL/SQL block