Что такое NULL? Сравнение с пустой строкой (10 мин.)

select 1, 5+6, 1=6;

select null = 'Some string';
select '' = 'Some string';

select null || 'Some string';
select '' || 'Some string';

select
	*
from
	address
where
	address2 <> 'Moscow';

select
	*
from
	address a
where
	address2 <> 'Moscow'
	or address2 is null;

select
	*
from
	address a
where
	address2 = null;

select '' = '';
select null = null;
select null = '';
select 1=1 and null = '';
select 1=1 or null = '';

select
	*
from
	address a
where
	address2 in ('Moscow', '', null)