What was the average unit price of products shipped via United Package in 1997?
via United Package refers to CompanyName = 'United Package'; in 1997 refers to OrderDate > = '1997-01-01 00:00:00' AND OrderDate < '1998-01-01 00:00:00'; average unit price = divide(sum(UnitPrice), count(ShipperID))
SELECT AVG(T2.UnitPrice) FROM Orders AS T1 INNER JOIN `Order Details` AS T2 ON T1.OrderID = T2.OrderID INNER JOIN Shippers AS T3 ON T1.ShipVia = T3.ShipperID WHERE T1.OrderDate LIKE '1997%' AND T3.CompanyName = 'United Package'