SELECT DISTINCT zip_code FROM weather EXCEPT SELECT DISTINCT zip_code FROM weather WHERE max_dew_point_f  >=  70
Find all the zip codes in which the max dew point have never reached 70.
SELECT DISTINCT zip_code FROM weather EXCEPT SELECT DISTINCT zip_code FROM weather WHERE max_dew_point_f > = 70
select distinct zip_code from weather except select distinct zip_code from weather where max_dew_point_f > = value
Find all the zip codes in which the max dew point have never reached 70 .