survey_sends (send_id, campaign, customer_id, rating) has one row per survey emailed out. rating is the score the customer gave (1–5), or NULL if they never answered.
For each campaign, report:
- •
sent: how many surveys went out - •
responses: how many came back with a rating - •
avg_rating: the average rating of the people who answered, rounded to 2 decimal places (NULL when nobody answered)
Columns: campaign, sent, responses, avg_rating. Sort by campaign.