Why doesn't SQL support “= null” instead of “is null”?

Question

I\'m not asking if it does. I know that it doesn\'t.

I\'m curious as to the reason. I\'ve read support docs such as as this one on Working With Nu

Answer 1

The reason why it's off by default is that null is really not equal to null in a business sense. For example, if you were joining orders and customers:

select * from orders o join customers c on c.name = o.customer_name

It wouldn't make a lot of sense to match orders with an unknown customer with customers with an unknown name.

Most databases allow you to customize this behaviour. For example, in SQL Server:

set ansi_nulls on
if null = null  
    print 'this will not print' 
set ansi_nulls off
if null = null  
    print 'this should print'