PL/SQL Variables

Summary: in this tutorial, you will learn about PL/SQL variables and how to use them effectively.

In PL/SQL, a variable is named storage location that stores a value of a particular data type. The value of the variable changes through the program. Before using a variable, you must declare it in the declaration section of a block.

Declaring variables

The syntax for a variable declaration is as follows:

variable_name datatype [NOT NULL] [:= initial_value];

In this syntax:

• First, specify the name of the variable. The name of the variable should be as descriptive as possible, e.g., l_total_sales, l_credit_limit, and l_sales_revenue.
• Second, choose an appropriate data type for the variable, depending on the kind of value which you want to store, for example, number, character, Boolean, and datetime.

By convention, local variable names should start with l_ and global variable names should have a prefix of g_ .

The following example declares three variables l_total_sales, l_credit_limit, and l_contact_name:

DECLARE
    l_total_sales NUMBER(15,2);
    l_credit_limit NUMBER (10,0);    
    l_contact_name VARCHAR2(255);
BEGIN
    NULL;
END;

Default values

PL/SQL allows you to set a default value for a variable at the declaration time. To assign a default value to a variable, you use the assignment operator (:=) or the DEFAULT keyword.

The following example declares a variable named l_product_name with an initial value 'Laptop':

DECLARE
  l_product_name VARCHAR2( 100 ) := 'Laptop';
BEGIN
  NULL;
END;

It is equivalent to the following block:

DECLARE 
   l_product_name VARCHAR2(100) DEFAULT 'Laptop';
BEGIN 
   NULL; 
END;

In this example, instead of using the assignment operator := , we used the DEFAULT keyword to initialize a variable.

NOT NULL constraint

If you impose the NOT NULL constraint on a value, then the variable cannot accept a NULL value. Besides, a variable declared with the NOT NULL must be initialized with a non-null value. Note that PL/SQL treats a zero-length string as a NULL value.

The following example first declares a variable named l_shipping_status with the NOT NULL constraint. Then, it assigns the variable a zero-length string.

DECLARE
  l_shipping_status VARCHAR2( 25 ) NOT NULL := 'Shipped';
BEGIN
  l_shipping_status := '';
END;

PL/SQL issued the following error:

ORA-06502: PL/SQL: numeric or value error

Because the variable l_shipping_status declared with the NOT NULL constraint, it could not accept a NULL value or zero-length string in this case.

Variable assignments

To assign a value to a variable, you use the assignment operator (:=), for example:

DECLARE
    l_customer_group VARCHAR2(100) := 'Silver';
BEGIN
    l_customer_group := 'Gold';
    DBMS_OUTPUT.PUT_LINE(l_customer_group);
END;

You can assign a value of a variable to another as shown in the following example:

DECLARE
    l_business_parter VARCHAR2(100) := 'Distributor';
    l_lead_for VARCHAR2(100);
BEGIN
    l_lead_for := l_business_parter; 
    DBMS_OUTPUT.PUT_LINE(l_lead_for);
END;

Anchored declarations

Typically, you declare a variable and select a value from a table column to this variable. If the data type of the table column changes, you must adjust the program to make it work with the new type.

PL/SQL allows you to declare a variable whose data type anchor to a table column or another variable. Consider the following example:

DECLARE
  l_customer_name customers.name%TYPE;
  l_credit_limit customers.credit_limit%TYPE;
BEGIN
  SELECT
    name, credit_limit
  INTO
    l_customer_name, l_credit_limit
  FROM
    customers
  WHERE
    customer_id = 38;

  DBMS_OUTPUT.PUT_LINE(l_customer_name || ':' || l_credit_limit );
END;
/

In this example:

• First,  declare two variables l_customer_name and l_credit_limit whose data type anchors to the name and credit_limit columns respectively, in the declaration section of the block.
• Second, query customer name and credit limit of the customer id 38 and assign these column values to the l_customer_name and l_credit_limit variables in the execution block.
• Third, display the customer name and credit limit.

PL/SQL returned the following output:

Kraft Heinz:500

This example illustrates how to declare variables that anchor to another variable:

DECLARE
    l_credit_limit   customers.credit_limit%TYPE;
    l_average_credit l_credit_limit%TYPE;
    l_max_credit     l_credit_limit%TYPE;
    l_min_credit     l_credit_limit%TYPE;
BEGIN
    -- get credit limits
    SELECT 
        MIN(credit_limit), 
        MAX(credit_limit), 
        AVG(credit_limit)
    INTO 
        l_min_credit,
        l_max_credit, 
        l_average_credit
    FROM customers;
    
    
    SELECT 
        credit_limit
    INTO 
        l_credit_limit
    FROM 
        customers
    WHERE 
        customer_id = 100;

    -- show the credits     
    dbms_output.put_line('Min Credit: ' || l_min_credit);
    dbms_output.put_line('Max Credit: ' || l_max_credit);
    dbms_output.put_line('Avg Credit: ' || l_average_credit);

    -- show customer credit    
    dbms_output.put_line('Customer Credit: ' || l_credit_limit);
END;

Here is the output:

Min Credit: 100
Max Credit: 5000
Avg Credit: 1894.67
Customer Credit: 1894.67

Now, you should know how to use PL/SQL variables in your block and manipulate them efficiently.