Can't retrieve all labels via v2 API

What would be the best way to retrieve all of the labels in the v2 api. When I make the request:

api/2.0/search?q=SELECT+*+FROM+labels+WHERE+messages.id='38'

It returns fine. But I can't just return all labels with the request:

api/2.0/search?q=SELECT+*+FROM+labels

Is there a reason for that?