DEMO 4, Sql Server

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CREATE TABLE Contacts (ContactID INT, EmailAddress VARCHAR(MAX), FirstName VARCHAR(MAX), LastName VARCHAR(MAX), [Address] VARCHAR(MAX))
CREATE TABLE Orders (OrderID INT, ContactID INT)

INSERT INTO Contacts VALUES 
(1, 'email1@email.com', 'Oldest', 'User', 'Oldest Address'),
(2, 'email2@email.com', 'Oldest', 'User', 'Oldest Address'),
(3, 'email3@email.com', 'Oldest', 'User', 'Oldest Address'),
(4, 'email4@email.com', 'Oldest', 'User', 'Oldest Address'),
(5, 'email1@email.com', 'Newest', 'User', 'Newest Address'),
(6, 'email2@email.com', 'Newest', 'User', 'Newest Address')

INSERT INTO Orders VALUES
(1, 1),
(2, 1),
(3, 2),
(4, 2),
(5, 3),
(6, 3),
(7, 4),
(8, 5),
(9, 6),
(10, 6)

SELECT	EmailAddress,
		FirstName,
		Lastname,
		[Address],
		NumOrders
FROM	(SELECT	c.EmailAddress,
				c.FirstName,
				c.LastName,
				c.[Address],
				COUNT(o.OrderID) OVER (PARTITION BY c.EmailAddress) NumOrders,
				ROW_NUMBER() OVER (PARTITION BY c.EmailAddress ORDER BY c.ContactID DESC) Rn
		FROM	Contacts c
				JOIN Orders o ON c.ContactID = o.ContactID
		) t
WHERE Rn = 1

View schema
Execution time: 0,08 sec, rows selected: 4, rows affected: 16, absolute service time: 0,23 sec