Ref T12974. Ferret object queries SELECT a virtual "_ft_rank" column for relevance ordering.
Currently, they always SELECT this column. That's fine and doesn't hurt anything, but makes developing and debugging things kind of a pain since every query has this , blah blah _ft_rank junk.
Instead, construct this column only if we're actually going to use it.
Mostly, this cleans up DarkConsole / query logs a bit.