Oh, and I would use <> 0 instead of = -1 unless the field can have other possible values.
I would bet you only got the -1 in there when you converted from Access YES/NO field to MySQL, yes? I'd be sorely tempted to change all the -1's to just 1 in the DB, but that's up to you.
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.