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'