How many stations were able to sell item 5 on January 2014?
item 5 refers to item_nbr = 5; on January 2014 refers to Substring (date, 1, 7) = '2014-01'
SELECT COUNT(DISTINCT T2.station_nbr) AS number FROM sales_in_weather AS T1 INNER JOIN relation AS T2 ON T1.store_nbr = T2.store_nbr WHERE SUBSTR(`date`, 1, 7) = '2014-01' AND item_nbr = 5