How many items weren't sold in store 2 on 1/1/2012?
store no.2 refers to store_nbr = 2; item weren't sold refers to units = 0; on 1/1/2012 refers to date = '2012-01-01'
SELECT COUNT(item_nbr) FROM sales_in_weather WHERE store_nbr = 2 AND units = 0 AND `date` = '2012-01-01'