Question

I have a row full of 1, 2, 3 and null. Why don’t there two return the same result:

select * from foo where foobar not in (1, 2, 3);
select * from foo where foobar is not null;

The first one returns empty set, while second one works as advertised. Now I’m a bit confused 😀 Is there some kind of “NULL in SQL for newbies” document anywhere? 😀

(I’m using Oracle, if that matters)

Answer 1

It’s because your first statement is being evaluated like this:

select * from foo
where foobar <> 1 and foobar <> 2 and foobar <> 3

“null <> 1” evaluates to null, not true/false, so nothing is returned.