What's the average low temperature of Monday?
select avg(low_temperature) from weekly_weather where day_of_week = "Monday";
How about its average high temperature?
select avg(high_temperature) from weekly_weather where day_of_week = "Monday";
Show me the average high temperature for each day of week?
select avg(high_temperature), day_of_week from weekly_weather group by day_of_week;