Oracle PL/SQL Programming, 5th Edition

Declaring Program Data

With few exceptions, you must declare your variables and constants before you use them. These declarations are in the declaration section of your PLSQL program. (See Chapter 3 for more details on the structure of the PL/SQL block and its declaration section.)

Your declarations can include variables, constants, TYPEs (such as collection types or record types), and exceptions. This chapter focuses on the declarations of variables and constants. (See Chapter 11 for an explanation of TYPE statements for records and Chapter 12 for collection types. See Chapter 6 to learn how to declare exceptions.)

Declaring a Variable

When you declare a variable, PL/SQL allocates memory for the variable’s value and names the storage location so that the value can be retrieved and changed. The declaration also specifies the datatype of the variable; this datatype is then used to validate values assigned to the variable.

The basic syntax for a declaration is:

name datatype [NOT NULL] [ := | DEFAULT default_assignment];

where name is the name of the variable or constant to be declared, and datatype is the datatype or subtype that determines the type of data that can be assigned to the variable. You can include a NOT NULL clause, which tells the database to raise an exception if no value is assigned to this variable. The [default_assignment] clause tells the database to initialize the variable with a value; this is optional for all declarations except those of constants. If you declare ...