query_sample

SELECT  
    date_trunc('hour', dt) dt,
    ((array_agg(bid ORDER BY dt ASC))[1] +
     (array_agg(ask ORDER BY dt ASC))[1])/2 o,
    (MAX(bid) + MAX(ask))/2 h,
    (MIN(bid) + MIN(ask))/2 l,
    ((array_agg(bid ORDER BY dt DESC))[1] +
     (array_agg(ask ORDER BY dt DESC))[1])/2 c,
    SUM(bid_vol) bid_vol,
    SUM(ask_vol) ask_vol,
    COUNT(*) ticks
FROM EURUSD  
WHERE dt >= '2017-07-01' 
GROUP BY date_trunc('hour', dt)  
ORDER BY dt DESC
LIMIT 5;

dt           |           o            |           h            |           l            |           c            |   bid_vol   |   ask_vol   | ticks
------------------------+------------------------+------------------------+------------------------+------------------------+-------------+-------------+-------
 2017-10-24 23:00:00-07 | 1.17646000000000000000 | 1.17659500000000000000 | 1.17580500000000000000 | 1.17601500000000000000 |  3305130000 |  3114120000 |  1416
 2017-10-24 22:00:00-07 | 1.17638000000000000000 | 1.17701000000000000000 | 1.17636500000000000000 | 1.17646500000000000000 |  3559260000 |  3777400000 |  1901
 2017-10-24 21:00:00-07 | 1.17611500000000000000 | 1.17654500000000000000 | 1.17606500000000000000 | 1.17637500000000000000 |  4837150000 |  4910810000 |  3194
 2017-10-24 20:00:00-07 | 1.17599500000000000000 | 1.17659000000000000000 | 1.17593500000000000000 | 1.17613000000000000000 |  4272990000 |  5269880000 |  2104
 2017-10-24 19:00:00-07 | 1.17852500000000000000 | 1.17928500000000000000 | 1.17581500000000000000 | 1.17600500000000000000 | 19965819993 | 19465699999 |  7968
(5 rows)