What was the total unit sold for item 10 when the average temperature was below the median temperature?
item 10 refers to item_nbr = 10; average temperature below median temperature refers to tavg < avg(tavg); total units refers to Sum(units)
SELECT SUM(T5.units) FROM weather AS T4 INNER JOIN sales_in_weather AS T5 ON T4.`date` = T5.`date` INNER JOIN relation AS T6 ON T5.store_nbr = T6.store_nbr WHERE T5.item_nbr = 10 AND T4.tavg < ( SELECT AVG(T1.tavg) FROM weather AS T1 INNER JOIN sales_in_weather AS T2 ON T1.`date` = T2.`date` INNER JOIN relation AS T3 ON T2.store_nbr = T3.store_nbr WHERE T2.item_nbr = 10 )