OK, I've absolutely no idea what's going on here with EXPLAIN.
I've had a look around, trying to understand, but it's so beyond me, I don't even know where to begin.
Right now, I don't even know what I don't understand, which is troubling.
There's just far too much to learn and I simply don't have the time to commit to this project, when client work is more pressing.
I can't expect people to just do all of this for me, so I think the best thing to do is call the whole thing off, and then come back to this, perhaps, at some later date.
Guys, thanks for your time! Always appreciated.