Variable Definition Statements

This section describes the declaration of variables in the PL/SQL and the scope of this variable in codes.

Variable Declaration

For details about the variable declaration syntax, see Figure 1.

Figure 1 declare_variable::=

The above syntax diagram is explained as follows:

variable_name indicates the name of a variable.
type indicates the type of a variable.
value indicates the initial value of the variable. (If the initial value is not given, NULL is taken as the initial value.) value can also be an expression.

Examples

openGauss=# DECLARE
    emp_id  INTEGER := 7788; -- Define a variable and assign a value to it.
BEGIN
    emp_id := 5*7784; -- Assign a value to the variable.
END;
/

In addition to the declaration of basic variable types, %TYPE and %ROWTYPE can be used to declare variables related to table columns or table structures.

%TYPE Attribute

%TYPE declares a variable to be of the same data type as a previously declared variable (for example, a column in a table). For example, if you want to define a my_name variable whose data type is the same as the data type of the firstname column in the employee table, you can define the variable as follows:

my_name employee.firstname%TYPE

In this way, you can declare my_name without the need of knowing the data type of firstname in employee, and the data type of my_name can be automatically updated when the data type of firstname changes.

TYPE employee_record is record (id INTEGER, firstname VARCHAR2(20));
my_employee employee_record;
my_id my_employee.id%TYPE;
my_id_copy my_id%TYPE;

%ROWTYPE Attribute

%ROWTYPE declares data types of a set of data. It stores a row of table data or results fetched from a cursor. For example, if you want to define a set of data with the same column names and column data types as the employee table, you can define the data as follows:

my_employee employee%ROWTYPE

The attribute can also be used on the cursor. The column names and column data types of this set of data are the same as those of the employee table. For the cursor in a package, %ROWTYPE can be omitted. %TYPE can also reference the type of a column in the cursor. You can define the data as follows:

cursor cur is select * from employee;
my_employee cur%ROWTYPE
my_name cur.firstname%TYPE
my_employee2 cur -- For the cursor defined in a package, %ROWTYPE can be omitted.

NOTICE:
%TYPE cannot reference the type of a composite variable or a record variable, a column type of the record type, a column type of a variable of the cross-package composite type, or a column type of a cursor variable of the cross-package type.
%ROWTYPE cannot reference the type of a composite variable or a record variable and the type of a cross-package cursor.

Scope of a Variable

The scope of a variable indicates the accessibility and availability of the variable in code block. In other words, a variable takes effect only within its scope.

To define a function scope, a variable must declare and create a BEGIN-END block in the declaration section. The necessity of such declaration is also determined by block structure, which requires that a variable has different scopes and lifetime during a process.
A variable can be defined multiple times in different scopes, and inner definition can cover outer one.
A variable defined in an outer block can also be used in a nested block. However, the outer block cannot access variables in the nested block.