Table: air_quality_index
Columns: c_low
c_high
i_low
i_high
category

Question: How many different C_{high} values are there for the good category?
SQL: SELECT COUNT("c_high") FROM air_quality_index WHERE "category" = 'Good'

Question: What's the C_{high} when the C_{low} value is 250.5?
SQL: SELECT "c_high" FROM air_quality_index WHERE "c_low" = '250.5'

Question: What's the i_{high} value when C_{low} is 250.5?
SQL: SELECT MIN("i_high") FROM air_quality_index WHERE "c_low" = '250.5'

Question: What's the C_{low} value when C_{high} is 12.0?
SQL: SELECT "c_low" FROM air_quality_index WHERE "c_high" = '12.0'

Question: In how many different categories is the value of C_{low} 35.5?
SQL: SELECT COUNT("category") FROM air_quality_index WHERE "c_low" = '35.5'