The value is missing for 'opened' events:
SELECT event_action, COUNT(*) AS frequency FROM log.Popups_16364296 WHERE wiki ='ruwiki' # the wiki with the most events AND event_isAnon AND DATE(timestamp) >= '2017-05-20' AND DATE(timestamp) <= '2017-05-24' AND event_popupEnabled AND event_linkInteractionToken IS NOT NULL AND event_perceivedWait IS NOT NULL GROUP BY event_action; +--------------+-----------+ | event_action | frequency | +--------------+-----------+ | dismissed | 26233 | +--------------+-----------+ 1 row in set (10.86 sec)