For each zip code, select all those that have an average mean visiblity below 10.
SELECT zip_code FROM weather GROUP BY zip_code HAVING avg(mean_visibility_miles)  <  10
SELECT zip_code FROM weather GROUP BY zip_code HAVING avg(mean_visibility_miles)  <  10
[{'zip_code': 94041}, {'zip_code': 94063}, {'zip_code': 94107}, {'zip_code': 95113}]