SELECT
    CONCAT(DATE(dumper_cycles.t_stamp), ' ', HOUR(dumper_cycles.t_stamp), ':00') AS StartTimestamp,
    CONCAT('H', TIMESTAMPDIFF(HOUR, DATE_FORMAT(dumper_cycles.t_stamp, "%Y-%m-%d %H:00:00"), DATE_FORMAT(NOW(), "%Y-%m-%d %H:00:00"))) AS Hour,
    CONCAT(ROUND(COALESCE(SUM(dumper_cycles.ulc1 = 1), 0)/COUNT(*) * 100*2, 2),'%') AS ULC1,
    CONCAT(ROUND(COALESCE(SUM(dumper_cycles.ulc2 = 1), 0)/COUNT(*) * 100*2, 2),'%') AS ULC2,
    CONCAT(ROUND(COALESCE(SUM(dumper_cycles.ulc3 = 1), 0)/COUNT(*) * 100*2, 2),'%') AS ULC3,
    CONCAT(ROUND(COALESCE(SUM(dumper_cycles.ulc4 = 1), 0)/COUNT(*) * 100*2, 2),'%') AS ULC4

FROM dumper_cycles
WHERE (dumper_cycles.t_stamp BETWEEN :starttime AND :endtime)
GROUP BY HOUR(dumper_cycles.t_stamp)

UNION ALL

-- Default row with zeros when no dumper cycles exist
SELECT
    CONCAT(DATE(:starttime), ' ', HOUR(:starttime), ':00') AS StartTimestamp,
    CONCAT('H', TIMESTAMPDIFF(HOUR, DATE_FORMAT(:starttime, "%Y-%m-%d %H:00:00"), DATE_FORMAT(NOW(), "%Y-%m-%d %H:00:00"))) AS Hour,
    '0%' AS ULC1,
    '0%' AS ULC2,
    '0%' AS ULC3,
    '0%' AS ULC4

WHERE NOT EXISTS (
    SELECT 1 FROM dumper_cycles
    WHERE dumper_cycles.t_stamp BETWEEN :starttime AND :endtime
);