Which station sold the highest quantity of item number 5 overall?
item number 5 refers to item_nbr = 5; sold highest quantity refers to Max(Sum(units)); station refers to station_nbr
SELECT T2.station_nbr FROM sales_in_weather AS T1 INNER JOIN relation AS T2 ON T1.store_nbr = T2.store_nbr WHERE T1.item_nbr = 5 GROUP BY T2.station_nbr ORDER BY SUM(T1.units) DESC LIMIT 1