-- zad2 OK
SELECT	SalesPersonID pracID,
		LastName + ',' + FirstName "Nazwisko , Imię",
		AVG(SubTotal) "Średnia psrzedaż",
		ROW_NUMBER() OVER (ORDER BY AVG(SubTotal) DESC) AS Ranking,
		CASE (NTILE(2) OVER(ORDER BY AVG(SubTotal) DESC))
			WHEN 1 THEN 'Wyróżniony'
			WHEN 2 THEN 'Do weryfikacji'
		END "Grupa"
FROM	Sales.SalesOrderHeader JOIN Person.Person ON SalesPersonID = BusinessEntityID
GROUP BY SalesPersonID, LastName , FirstName
ORDER BY 3 DESC, 2, 1;

-- zad3 OK
SELECT	YEAR(OrderDate) Rok,
		MONTH(OrderDate) Miesiąc,
		DAY(OrderDate) Dzień,
		SUM(Sales.SalesOrderHeader.SubTotal) Kwota,
		COUNT(*) "Liczba zamówień"
FROM	Sales.SalesOrderHeader
GROUP BY ROLLUP(YEAR(OrderDate), MONTH(OrderDate), DAY(OrderDate))
HAVING YEAR(OrderDate) IS NOT NULL AND MONTH(OrderDate) IS NOT NULL AND DAY(OrderDate) IS NOT NULL
ORDER BY 1, 2, 3

-- zad4 OK
SELECT	SalesPersonID pracID,
		CustomerID klientID,
		ROUND(SUM(SubTotal),2) Suma
FROM	Sales.SalesOrderHeader
GROUP BY ROLLUP(SalesPersonID, CustomerID)
ORDER BY 1, 2, 3 DESC