SET group_concat_max_len = 10485760;
SELECT * FROM (SELECT concat(substring(event_uploadTimestamp, 1, 4), '-', substring(event_uploadTimestamp, 5, 2)) AS datestring FROM (
SELECT event_uploadTimestamp FROM MultimediaViewerNetworkPerformance_10596581
WHERE event_uploadTimestamp < TIMESTAMP(CURDATE()) AND event_uploadTimestamp >= TIMESTAMP(DATE_SUB(CURDATE(), INTERVAL 730 DAY))
UNION ALL
SELECT event_uploadTimestamp FROM MultimediaViewerNetworkPerformance_10774577
WHERE event_uploadTimestamp < TIMESTAMP(CURDATE()) AND event_uploadTimestamp >= TIMESTAMP(DATE_SUB(CURDATE(), INTERVAL 730 DAY))
) AS MultimediaViewerNetworkPerformanceUnioned GROUP BY datestring ORDER BY datestring ASC) dates

LEFT OUTER JOIN

( SELECT concat(substring(event_uploadTimestamp, 1, 4), '-', substring(event_uploadTimestamp, 5, 2)) AS datestring,
EXP(AVG(LOG(event_total))) AS image_time_mean,
EXP(STD(LOG(event_total))) AS image_time_std,
COUNT(*) AS image_sample_size,
CAST(SUBSTRING_INDEX(SUBSTRING_INDEX(
  GROUP_CONCAT(event_total ORDER BY event_total SEPARATOR ','),
   ',', 1/100 * COUNT(*) + 1), ',', -1) AS DECIMAL) AS image_time_1st_percentile,
CAST(SUBSTRING_INDEX(SUBSTRING_INDEX(
  GROUP_CONCAT(event_total ORDER BY event_total SEPARATOR ','),
   ',', 50/100 * COUNT(*) + 1), ',', -1) AS DECIMAL) AS image_time_50th_percentile,
CAST(SUBSTRING_INDEX(SUBSTRING_INDEX(
  GROUP_CONCAT(event_total ORDER BY event_total SEPARATOR ','),
   ',', 90/100 * COUNT(*) + 1), ',', -1) AS DECIMAL) AS image_time_90th_percentile,
CAST(SUBSTRING_INDEX(SUBSTRING_INDEX(
  GROUP_CONCAT(event_total ORDER BY event_total SEPARATOR ','),
   ',', 95/100 * COUNT(*) + 1), ',', -1) AS DECIMAL) AS image_time_95th_percentile,
CAST(SUBSTRING_INDEX(SUBSTRING_INDEX(
  GROUP_CONCAT(event_total ORDER BY event_total SEPARATOR ','),
   ',', 99/100 * COUNT(*) + 1), ',', -1) AS DECIMAL) AS image_time_99th_percentile FROM (
SELECT event_type, event_total, event_uploadTimestamp, wiki FROM MultimediaViewerNetworkPerformance_10596581
WHERE event_uploadTimestamp < TIMESTAMP(CURDATE()) AND event_uploadTimestamp >= TIMESTAMP(DATE_SUB(CURDATE(), INTERVAL 730 DAY)) AND event_total > 20 AND event_type = 'image' AND ( event_varnish1hits > 0 OR event_varnish2hits > 0 OR event_varnish3hits > 0)
UNION ALL
SELECT event_type, event_total, event_uploadTimestamp, wiki FROM MultimediaViewerNetworkPerformance_10774577
WHERE event_uploadTimestamp < TIMESTAMP(CURDATE()) AND event_uploadTimestamp >= TIMESTAMP(DATE_SUB(CURDATE(), INTERVAL 730 DAY)) AND event_total > 20 AND event_type = 'image' AND ( event_varnish1hits > 0 OR event_varnish2hits > 0 OR event_varnish3hits > 0)
) AS MultimediaViewerNetworkPerformanceUnioned GROUP BY datestring ORDER BY datestring ASC ) stats USING (datestring)