It's also dangerous to use * in advanced Queries, mainly because the actually order of attributes might not be the same with the visual order of the attributes.
so, like the others, don;t use *, unless you are very sure.
if you are sure, the warning simply tells you service-studio is unable to verify it, and you simply hide the message :D
(on that note, if the sql is that simple, you actually are better off with an aggregate)