SELECT zip_code FROM weather GROUP BY zip_code HAVING avg(mean_visibility_miles)  <  10
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 ) < value
For each zip code , select all those that have an average mean visiblity below 10 .