MySQL mystery: Null value is not different from non-null string

Question

Why is this query returning 0 rows?

select t.f1, t.f2
from (select null f1, \'a\' f2 from dual) t
where t.f1<>t.f2;

This is a distill

Answer 1

SQL NULL does not work the way you would like it to work: http://en.wikipedia.org/wiki/Sql_null

In short, NULL = NULL is not true. NULL <> NULL is not true. NULL <> 1 is not true. And so forth.