I'm running a very simple query that I think should work. The only thing that I haven't done before is put a php variable in the WHERE clause of the query. The variable $X is a numerical value, say 100. When I run this query, I just get a value of 0 returned. Am I doing something obviously stupid?

SELECT generator_64k.n
FROM generator_64k
WHERE generator_64k.n<= '$X'

I've looked around the web and also tried this:

SELECT generator_64k.n
FROM generator_64k
WHERE generator_64k.n<= '" . $X . "'

But this also just returns 0.

Any ideas? Thanks in advance.