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  >=  70
[{'zip_code': 94063}, {'zip_code': 94107}, {'zip_code': 95113}]