How many units of item 7 have been sold by store 7 when the snow is less than 5 inches?
item 7 refers to item_nbr = 7; store 7 refers to store_nbr = 7; snow is less than 5 inches refers to snowfall < 5
SELECT SUM(units) 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 T2.store_nbr = 7 AND T3.item_nbr = 7 AND T1.snowfall < 5