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A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in PL/SQL has a specific data type, which determines the size and layout of the variable's memory; the range of values that can be stored within that memory and the set of operations that can be applied to the variable.
The name of a PL/SQL variable consists of a letter optionally followed by more letters, numerals, dollar signs, underscores, and number signs and should not exceed 30 characters. By default, variable names are not case-sensitive. You cannot use a reserved PL/SQL keyword as a variable name.
PL/SQL programming language allows to define various types of variables, which we will cover in subsequent chapters like date time data types, records, collections, etc. For this chapter, let us study only basic variable types.
With PL/SQL you can declare variables and then use them in SQL and procedural statements anywhere that an expression can be used. Variables can be used for the following:
• Temporary storage of data: Data can be temporarily stored in one or more variables for use when validating data input and for processing later in the data flow process.
• Manipulation of stored values: Variables can be used for calculations and other data manipulations without accessing the database.
• Reusability: After they are declared, variables can be used repeatedly in an application simply by referencing them in other statements, including other declarative statements.
• Ease of maintenance: When using %TYPE and %ROWTYPE (more information on %ROWTYPE is covered in a subsequent lesson), you declare variables, basing the declarations on the definitions of database columns. If an underlying definition changes, the variable declaration changes accordingly at run time. This provides data independence, reduces maintenance costs, and allows programs to adapt as the database changes to meet new business needs. More information on %TYPE is covered later in this lesson.
Types of Variables"
All PL/SQL variables have a data type, which specifies a storage format, constraints, and valid range of values. PL/SQL supports four data type categories—scalar, composite, reference, and LOB (large object)—that you can use for declaring variables, constants, and pointers.
• Scalar data types hold a single value. The main data types are those that correspond to column types in Oracle server tables; PL/SQL also supports Boolean variables.
• Composite data types, such as records, allow groups of fields to be defined and manipulated in PL/SQL blocks.
• Reference data types hold values, called pointers, that designate other program items. Reference data types are not covered in this course.
• LOB data types hold values, called locators, that specify the location of large objects (such as graphic images) that are stored out of line. LOB data types are discussed in detail later in this course.