Select EmployeeID,
(Select count(OrderID)
from Orders where EmployeeID = E.EmployeeID)
from Employees E

Select C.CategoryID, C.CategoryName, AVG(P.UnitPrice)
From Products P, Categories C Where P.CategoryID = C.CategoryID
Group by C.CategoryID, C.CategoryName

Select * from Customers
Select * from Orders

Select C.CustomerID, C.ContactName, Count(O.OrderID)
From Customers C, Orders O Where C.CustomerID=O.CustomerID and year(ShippedDate)='1997'
Group by C.CustomerID, C.ContactName