SQL IS NULL

List customers that have not placed any orders.

SELECT C.Id, FirstName, LastName, TotalAmount
  FROM Customer C
  LEFT JOIN [Order] O ON C.Id = O.CustomerId
 WHERE TotalAmount IS NULL

IS NULL syntax.

SELECT column-names
  FROM table-name
 WHERE column-name IS NULL

IS NOT NULL syntax.

SELECT column-names
  FROM table-name
 WHERE column-name IS NOT NULL

SELECT Id, CompanyName, Phone, Fax 
  FROM Supplier
 WHERE Fax IS NULL

Id	CompanyName	Phone	Fax
1	Exotic Liquids	(171) 555-2222	NULL
2	New Orleans Cajun Delights	(100) 555-4822	NULL
4	Tokyo Traders	(03) 3555-5011	NULL
5	Cooperativa de Quesos 'Las Cabras'	(98) 598 76 54	NULL
6	Mayumi's	(06) 431-7877	NULL

SELECT Id, CompanyName, Phone, Fax 
  FROM Supplier
 WHERE Fax IS NOT NULL

• Our Sql WHERE IN Tutorial
• Our Sql WHERE EXISTS Tutorial
• Our Sql NULLIF Function Reference