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:
Code language: SQL (Structured Query Language) (sql)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
, andl_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;
Code language: SQL (Structured Query Language) (sql)
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;
Code language: SQL (Structured Query Language) (sql)
It is equivalent to the following block:
DECLARE
l_product_name VARCHAR2(100) DEFAULT 'Laptop';
BEGIN
NULL;
END;
Code language: SQL (Structured Query Language) (sql)
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;
Code language: SQL (Structured Query Language) (sql)
PL/SQL issued the following error:
Code language: SQL (Structured Query Language) (sql)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;
Code language: SQL (Structured Query Language) (sql)
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;
Code language: SQL (Structured Query Language) (sql)
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;
/
Code language: SQL (Structured Query Language) (sql)
In this example:
- First, declare two variables
l_customer_name
andl_credit_limit
whose data type anchors to thename
andcredit_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 thel_customer_name
andl_credit_limit
variables in the execution block. - Third, display the customer name and credit limit.
PL/SQL returned the following output:
Code language: SQL (Structured Query Language) (sql)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;
Code language: SQL (Structured Query Language) (sql)
Here is the output:
Code language: SQL (Structured Query Language) (sql)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.