SQL uses ternary logic. This means that a conditional statement can evaluate
to TRUE, FALSE, or NULL (unknown). Whaaaa? 😮 And somehow NULL
is still 'falsy'? Unfortunately, this won't be the only time you run into logic
that defies intuition. Stay tuned for Javascript quirks.
Asking if a NULL value = NULL will always produce FALSE. This is because
NULL was derived to represent an unknown value. How can we know if two
unknowns are the same? We can't. Given that this sort of comparison doesn't
yield any useful information, always use IS NULL or IS NOT NULL in place of
the traditional (= or != / <>) comparisons.