Which weather station does the store that sold the highest quantity of item 9 belongs to?
item 9 refers to item_nbr = 9; sold the highest quantity refers to Max(Sum(units)); weather station refers to station_nbr
SELECT station_nbr FROM sales_in_weather AS T1 INNER JOIN relation AS T2 ON T1.store_nbr = T2.store_nbr WHERE T1.item_nbr = 9 GROUP BY T2.station_nbr ORDER BY SUM(T1.units) DESC LIMIT 1