SQL IS NULL Clause

What is NULL and how do I query for NULL values?

• NULL is a special value that signifies 'no value'.
• Comparing a column to NULL using the = operator is undefined.
• Instead, use WHERE IS NULL or WHERE IS NOT NULL.

The SQL WHERE IS NULL syntax

The general IS NULL syntax is

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

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

SQL WHERE IS NULL Examples

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