1.
SELECT Sum(Price) FROM Products;
SELECT Avg(Price) FROM Products;
SELECT Count(OrderID) FROM Orders;
SELECT Max(Quantity) FROM OrderDetails
Select * from products where price = (SELECT min(Price) FROM [Products])
Select ProductID from products where price = (SELECT max(Price) FROM [Products])
Select avg(Quantity) from OrderDetails Where ProductID = (Select ProductID from products where price = (SELECT max(Price) FROM [Products]))

2.
SELECT AVG(Price), SupplierID FROM [Products] GROUP BY SupplierID
SELECT ProductID, AVG(Quantity) FROM [OrderDetails] Group By ProductID	
SELECT City,Count(City) FROM [Customers] Group By City

3.
SELECT * FROM Products, Categories WHERE Products.CategoryID = Categories.CategoryID
SELECT * FROM Orders, Customers WHERE Orders.CustomerID = Customers.CustomerID
SELECT * FROM Orders, Customers WHERE Orders.CustomerID = Customers.CustomerID and Orders.OrderDate='1996-12-31'

4.
SELECT ProductID, ProductName, SupplierID, Price FROM [Products] WHERE Price = (SELECT MAX(Price) from Products)
SELECT ProductID, MAX(Quantity) from OrderDetails Group By ProductID
ProductID 38, Max Quantity 50
SELECT * FROM [OrderDetails] WHERE ProductID=38 and Quantity=50
OrderID 10353
SELECT * FROM Orders, Customers WHERE Orders.CustomerID=Customers.CustomerID and OrderID=10353