App Click-through Rate (CTR).sql

SELECT
  app_id,
  ROUND(100.0 *
    SUM(CASE WHEN event_type = 'click' THEN 1 ELSE 0 END) /
    SUM(CASE WHEN event_type = 'impression' THEN 1 ELSE 0 END), 2)  AS ctr_rate
FROM events
WHERE timestamp >= '2022-01-01' 
  AND timestamp < '2023-01-01'
GROUP BY app_id;