SQL Null Values

The SQL NULL value means a field with no value present in it.

What is a SQL NULL Value?

If a field in a table is optional in other words if it’s not mandatory, it is possible to insert a new record or update a record without adding a value to this field. Then, the field will be saved with a NULL value.

Note:
“A NULL value is different from a zero value or a field that contains spaces. A field with a NULL value is one that has been left blank during record creation!”

    SELECT column_1, column_2
    FROM table_name
    WHERE column_1 IS NULL;
  

    SELECT column_1, column_2
    FROM table_name
    WHERE column_1 IS NOT NULL;
  

Query

Consider we have a customer table in which one record is having a null value and in another record all data is present.

IS NULL Operator
The IS NULL operator is used for checking empty values (NULL values).

SELECT * FROM customers WHERE address IS NULL;

-- 1 record found.
-- +-----------------------------------------+
-- |  customerID   | name         | address  |
-- |-----------------------------------------|
-- |  90           | White Clover | null     |
-- +-----------------------------------------+

IS NOT NULL Operator
The IS NOT NULL operator is used for checking non-empty values (NOT NULL values).

SELECT * FROM customers WHERE address IS NOT NULL;

-- 1 record found.
-- +-----------------------------------------------+
-- |  customerID   | name         | address        |
-- |-----------------------------------------------|
-- |  89           | Wilman Kala  | Keskuskatu 45  |
-- +-----------------------------------------------+

.
SQL Complete Guide