If the query_id* is null, it is not actually running yet. This is a good thing as far as your stated tracking requirements. You can do a WHERE query_id IS NOT NULL to exclude statements where the query has appeared, but has not been parsed and executed yet. I daresay you also want to be looking at wait_event and now()-state_change as well.
Cheers,
Greg
* Actually, query_id some places, queryid in others. So annoying.
