In March 2014, which weather stations recorded the highest number of days whose temperature is below the 30-year normal?
in March 2014 refers to substring (date, 1, 4) = '2014' and substring (date, 6, 2) = '03'; temperature is below the 30-year normal refers to depart < 0; highest number of days refers to Max(Count(date))
SELECT station_nbr FROM weather WHERE SUBSTR(`date`, 1, 4) = '2014' AND SUBSTR(`date`, 6, 2) = '03' AND depart < 0 GROUP BY station_nbr HAVING COUNT(DISTINCT `date`) = ( SELECT COUNT(DISTINCT `date`) FROM weather WHERE SUBSTR(`date`, 1, 4) = '2014' AND SUBSTR(`date`, 6, 2) = '03' AND depart < 0 GROUP BY station_nbr ORDER BY COUNT(`date`) DESC LIMIT 1 )