Interval and nearest match

SQL++
10 
SELECT q.panelid, q.sensorid, MILLIS_TO_STR(iv.interval) AS interval,
       MIN([ABS(STR_TO_MILLIS(el.timestamp)-iv.interval),el])[1] AS el FROM (
           SELECT d.panelid, d.sensorid,
               ARRAY_FLATTEN(ARRAY_AGG(ARRAY el FOR el IN d.data WHEN el.timestamp BETWEEN "2015-06-04T09:00:00" AND "2015-06-04T17:00:00" END),2) AS data,
               MIN(ARRAY {"interval": v} FOR v IN ARRAY_RANGE(STR_TO_MILLIS("2015-06-04T09:00:00"),STR_TO_MILLIS("2015-06-04T17:00:00"),str_to_duration("3h")/1000000) END) AS interval
        FROM default d
        WHERE panelid="a-si" and sensorid="voc" AND
              ANY el IN d.data SATISFIES el.timestamp BETWEEN "2015-06-04T09:00:00" AND "2015-06-04T17:00:00" END
        GROUP BY d.panelid, d.sensorid) AS q UNNEST q.interval AS iv UNNEST q.data AS el
GROUP BY  q.panelid, q.sensorid, iv.interval;