Nutrition Co., a health snack company, would like to know the total impressions that have been delivered per campaign, per supply_source, per device_type. Which of the following represents how to write this query?

• SELECT total_impressions SUM(impressions) AS device_type FROM campaign, supply_source GROUP BY 1,2,3
• SELECT campaign, supply_source, SUM(impressions) AS impressions FROM device_type GROUP BY 1,2
• SELECT campaign, supply_source, device_type, SUM(impressions) AS impressions FROM dsp_impressions GROUP BY 1,2,3

The correct answer is:

• SELECT campaign, supply_source, device_type, SUM(impressions) AS impressions FROM dsp_impressions GROUP BY 1,2,3