gistfile1.sql

select @rn:=@rn+1 as rank, referrals
from (
	select count(referrer_id) as referrals, referrer_id from users
	where referrer_id is not null
	group by referrer_id
	order by referrals desc) t1, (select @rn:=0) t2
	
-- Giving output like this
/* rank	referrals
	1		100
	2		99
	3		97
	4		50
	5		48
	6		42 */