pisemka

-- první dotaz

SELECT o.uID, o.jmeno, ob.oID, DATEDIFF(HOUR, ob.vytvorena, ob.potvrzena) rozdil
FROM osoba o
JOIN objednavka ob ON ob.uID = o.uID AND potvrzena IS NOT NULL
WHERE DATEDIFF(HOUR, ob.vytvorena, ob.potvrzena) <= ALL
(
    SELECT DATEDIFF(HOUR, ob2.vytvorena, ob2.potvrzena)
    FROM objednavka ob2
    WHERE ob2.uID = o.uID
          AND ob2.oID <> ob.oID
          AND ob2.potvrzena IS NOT NULL
)

-- druhý dotaz

SELECT uID, jmeno,
(
    SELECT COUNT(*)
    FROM objednavka ob
    WHERE ob.uID = o.uID AND
          potvrzena IS NOT NULL AND
          DATEDIFF(HOUR, vytvorena, potvrzena) < 1
) potvrzeno_do_hodiny,
(
    SELECT COUNT(*)
    FROM objednavka ob
    WHERE ob.uID = o.uID AND
          potvrzena IS NOT NULL AND
          DATEDIFF(HOUR, vytvorena, potvrzena) < 2
) potvrzeno_do_dvou_hodin
FROM osoba o

-- třetí dotaz

SELECT ob.oID
FROM objednavka ob
JOIN polozka p ON p.oID = ob.oID
JOIN zbozi z ON z.zID = p.zID
GROUP BY ob.oID
HAVING COUNT(*) / 2 < COUNT(CASE WHEN z.kategorie = 1 THEN 1 ELSE NULL END)