use examples

/* Method 1 - Sub-Queries */

select active, paid, count(*) as users
from
(
select conv_rate.*, active
from
	(
	select signed_up.*
		, case when (paid.username is not null) then 1 else 0 end as paid
	from
		(
		select *
		from subscriptions
		where plan_id = 0
		and year(subscription_start)*100+month(subscription_start) = 201411
		) signed_up
	left join
		(
		select subs.*
		from
			(
			select *
			from subscriptions
			where plan_id > 0
			) subs
			join
			(
			select username
				, min(subscription_start) as first_sub 
			from subscriptions 
			where plan_id>0 
			group by username
			) first_sub
		on subs.username = first_sub.username
		and subs.subscription_start = first_sub.first_sub
		) paid
	on signed_up.username = paid.username
	) conv_rate
left join
	(
	select su.username
		, max(case when (se.session_start between su.subscription_start and dateadd(dd,14,su.subscription_start)) then 1 else 0 end) as active
	from subscriptions su
	left join sessions se
	on su.username = se.username
	where su.plan_id = 0
	group by su.username
	) was_active
on conv_rate.username = was_active.username
) final_data
group by active, paid
order by active, paid