Let's suppose that I have the following PHP code in one of my files.

$myselect = "select * FROM thread WHERE forumid<>5 ORDER BY lastpost DESC LIMIT 10";

How do I also exclude threads where they come from forumid 18 or 19?

I tried:

$myselect = "select * FROM thread WHERE forumid<>5 OR forumid<>18 or forumid<>19 ORDER BY lastpost DESC LIMIT 10";

but it wouldn't work. Can someone tell me how do I do it the right way?