What is the most purchased products during the rainy days in June 2013 in weather station 9?
most purchased product refers to Max(units); during the rainy day refers to codesum = RA; in June 2013 refers to SUBSTR(date, 1, 7) = '2013-06'; weather station 9 refers to station_nbr = 9; product refers to item_nbr
SELECT T1.item_nbr FROM sales_in_weather AS T1 INNER JOIN relation AS T2 ON T1.store_nbr = T2.store_nbr INNER JOIN weather AS T3 ON T2.station_nbr = T3.station_nbr WHERE T3.station_nbr = 9 AND T1.`date` LIKE '%2013-06%' AND codesum = 'RA' ORDER BY T1.units DESC LIMIT 1