Tell the temperature range of the home weather station of store no.7 on 2014/4/28.
store no.7 refers to tore_nbr = 7; on 2014/4/28 refers to date = '2014-04-28'; temperature range refers to Subtract (tmax, tmin)
SELECT T1.tmax - T1.tmin AS temprange FROM weather AS T1 INNER JOIN relation AS T2 ON T1.station_nbr = T2.station_nbr WHERE T2.store_nbr = 7 AND T1.`date` = '2014-04-28'