The following query

		SELECT cust.CustName, pri.FullName, AS PrimaryContact, alt.FullName AS AlternateContact
		FROM Customers.cust
		JOIN People pri ON cust.PrimaryContactPersonID = pri.PersonID
		LEFT JOIN People alt on cust.AlternateContactPersonID = alt.PersonID
		will return:
		a) Customers with both primary and alternate contacts
		b) Customers with a primary contact and with or without alternate contacts
		c) Customers with a primary contact and without alternate contacts
		d) No rows