Question: How many items were sold by store 9 during a snowy day?
SQL: SELECT COUNT(DISTINCT item_nbr) FROM weather AS T1 INNER JOIN relation AS T2 ON T1.station_nbr = T2.station_nbr INNER JOIN sales_in_weather AS T3 ON T2.store_nbr = T3.store_nbr WHERE T3.store_nbr = 9 AND T1.snowfall <> 0 AND T1.snowfall IS NOT NULL