a field with a NULL value is a field with no value.
If a field in a table is optional, 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.
How to test for NULL values?
it is not possible to test for NULL values with comparison operator, such as = < or <>
We will have t o use the IS NULL and IS NOT NULL operator instead.
IN NULL syntax
SELECT column_names
FROM table_name
WHERE column_name IS NULL ;
IS NOT NULL syntax
SELECT colomn_names
FROM table_name
WHERE column_name IS NOT NULL ;
The demo database goes like below
IF i want to find the NULL Values from City
SELECT City
FROM Customers
WHERE City IS NULL ;
The result like that.
viceversa, IN NOT NULL with same condition
SELECT City
FROM Customers
WHERE City IS NOT NULL ;
SELECT CustomerName, address, Country
FROM Customers
WHERE Country IS NOT NULL ;