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

Try to do this query:

   select * from dual where NULL = NULL

It returns 0 rows. That's because to compare a value with null you have to do IS NULL or IS NOT NULL, otherwise it will return false.