select 
	u.iduser,u.login,count(f.idfile)
from 
	users u , folders d, files f
where 
	f.fk_idfolder = d.idfolder and 
	d.fk_iduser = u.iduser
group by 
	u.iduser,u.login
order by 
	u.login;


select 
	u.iduser,u.login,count(f.idfile)
from 
	users u  
		join folders d on (d.fk_iduser = u.iduser)
		join files f on (f.fk_idfolder = d.idfolder)
group by
	u.iduser,u.login
order by 
	u.login;

select 
	u.iduser,u.login,
	(
		select 
			count(f.idfile)
		from 
			folders d, files f
		where 
			f.fk_idfolder = d.idfolder and 
			d.fk_iduser = u.iduser
	) count_
from 
	users u 
group by 
	u.iduser,u.login
order by 
	u.login

select 
	u.iduser,u.login,
	(
		select 
			sum(
			(
				select 
					count(*) 
				from 
					files f 
				where 
					f.fk_idfolder = d.idfolder
			))
		from 
			folders d
		where 
			d.fk_iduser = u.iduser
	) as count_
from
	users u
order by
	u.login