Creating and using an index

You are working with the US air quality index (AQI) data. AQI data captures four pollutants: ozone, particle pollution, carbon monoxide, and sulfur dioxide. You want to know if one of these pollutants is the main source of poor air quality.

The daily_aqi table contains daily AQI measurements. The defining_parameter field describes which of the four pollutants was the worst for that day.

You will be writing a lot of queries using the pollutant type as a filter. Before you dig into the data, you want to check if defining_parameter has an index on it. If not, you want to add one.