//Non optymalized
select c1.cas,count(distinct c1.data) from casdat c1
where c1.type='sent'
group by c1.cas
having count(distinct c1.data)>
(select count(distinct c2.data) from casdat c2 where c2.type='rent' and c2.cas=c1.cas);

//Bugged optymalized
select c1.cas from
casdat c1 join casdat c2 on c1.cas=c2.cas
where c1.type='sent' and c2.type='rent'
group by c1.cas
having count(distinct c1.data)>count(distinct c2.data);

//Fixed optymalized
select c1.cas from
casdat c1 left outer join casdat c2 on (c1.cas=c2.cas and c2.type='rent')
where c1.type='sent'
group by c1.cas
having count(distinct c1.data)>count(distinct c2.data);