If there's only ever one client, that's fine. Otherwise, this contains a race condition that the OP does not have. Imagine two clients select, both see nothing, both try to insert, one fails. At that point, the one that failed to insert should update, exactly like what the OP is already doing (but without the select).

Update: It also occurs to me that if you're not concerned about a race condition, you could do something like this without the select. First try to update, then check to see how many rows were affected. If there weren't any, do the insert. As I say, this has a race condition also, but it will sometimes be one statement instead of always being two.