SELECT
  group_id, event, COUNT(*) AS events
FROM (
  SELECT DISTINCT
    event_uniqueId AS event_id,
    event_subTest AS group_id,
    event_action AS event
  FROM TestSearchSatisfaction2_16909631
  WHERE LEFT(timestamp, 8) >= '20170914'
    AND wiki = 'enwiki'
    AND event_subTest IN('explore_similar_control', 'explore_similar_test')
    AND event_source = 'fulltext'
) AS explore_similar
GROUP BY group_id, event;