udbs2 QQ

/*
select jmeno from vyrobek where vID in (

select vID from koupil
where login = 'vinetu' )

and

vID in(

select vID from koupil
where login = 'pepik'
)
*/
/*
select jmeno from vyrobek v
where not exists (select * from koupil k where k.vID = v.vID)
*/
/*
select jmeno from vyrobek
where vID not in (select vID from koupil k)
*/
/*
select jmeno from vyrobek where vID in (

select vID from koupil
where login = 'vinetu' )

and

vID not in(

select vID from koupil
where login = 'pepik'
)
*/
/*
select jmeno from vyrobek where vID in(
select vID from koupil group by login, vID having count(*) >=2)
*/
/*
select jmeno from vyrobek v where exists(
select * from koupil k where k.vID=v.vID group by login, vid having count(*)>=2 )
*/
/*
select v.jmeno from vyrobek v where aktualni_cena> all(select cena from koupil k where k.vID=v.vID)
*/

/*
select v.jmeno from vyrobek v where not exists (select * from koupil k where k.vID=v.vID and k.cena > v.aktualni_cena)
*/
/*
select login, count(*) from koupil group by login having count(*) = 1
*/
/*
select distinct v.jmeno from koupil k
join vyrobek v on v.vid = k.vId
where not exists(
select * from koupil k2
where k.vID != k2.vID and k2.login =k.login)

*/

/*
select distinct v.jmeno from koupil k
join vyrobek v on v.vID = k.vID
where not exists(
select * from koupil k2
where k.vID!=k2.vID and k2.login = k.login)
*/

/*
select *from r1 join r2 on r1.id = r2.id
*/

SELECT DISTINCT k.login FROM koupil k
WHERE cena <=ALL(SELECT cena FROM koupil k2 WHERE k2.login !=k.login AND k.vid = k2.vid)