On which day was the weather more windy in station no.1, 2012/1/1 or 2012/1/2?
station no.1 refers to station_nbr = 1; 2012/1/1 refers to date = '2012-01-01'; 2012/1/2 refers to date = '2012-01-02'; more windy refers to Max(avgspeed)
SELECT CASE WHEN (SUM(CASE WHEN `date` = '2012-01-01' THEN avgspeed ELSE 0 END) - SUM(CASE WHEN `date` = '2012-01-02' THEN avgspeed ELSE 0 END)) > 0 THEN '2012-01-01' ELSE '2012-01-02' END FROM weather WHERE station_nbr = 1