On the day with the highest max temperature in 2012, how many items in store no.3 had no sales?
highest max temperature refers to Max(tmax); in 2012 refers to SUBSTR(date, 1, 4) = '2012'; store no.3 refers to store_nbr = 3; had no sale refers to units = 0
SELECT COUNT(DISTINCT 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 AND T1.store_nbr = 3 AND SUBSTR(T1.`date`, 1, 4) = '2012' AND T1.units = 0 GROUP BY T3.tmax ORDER BY T3.tmax DESC LIMIT 1