SELECT variant, count(clientID) amount
FROM
(
  SELECT  clientId, SPLIT(experiment.experimentId,".")[OFFSET(2)] variant

  FROM
   `dokdbroker.OWOXBI_Streaming.streaming_*`
    WHERE true
      AND _TABLE_SUFFIX between "20171102" and "20171115"
      --AND SPLIT(experiment.experimentId,".")[OFFSET(1)] = "-mO_Is3YTEaafugnZkVpUA"
      --AND eventInfo.eventAction = "add-to-cart"
     AND (SELECT value FROM UNNEST(customGroups) WHERE index = 1) = "inside"
     AND (SELECT value FROM UNNEST(customGroups) WHERE index = 2) = "15"
  GROUP BY clientId, variant
)
GROUP BY variant