test.hits
SELECT *
FROM
(
SELECT
RegionID,
toDateTime(EventDate) AS date,
count() AS quantity
FROM test.hits
GROUP BY
RegionID,
date
) AS regions
ASOF LEFT JOIN
(
SELECT
RegionID,
EventTime
FROM test.hits
) AS ids ON (regions.RegionID = ids.RegionID) AND (regions.date < ids.EventTime)