-- Stale devices: enabled devices with no GPS fix in last 2 hours
SELECT
    d.imei,
    d.device_name,
    lp.gps_time                                      AS last_gps_time,
    EXTRACT(EPOCH FROM (NOW() - lp.gps_time)) / 3600 AS hours_since_fix
FROM tracksolid.devices d
LEFT JOIN tracksolid.live_positions lp ON lp.imei = d.imei
WHERE d.enabled_flag = 1
  AND (
      lp.gps_time IS NULL
      OR lp.gps_time < NOW() - INTERVAL '2 hours'
  )
ORDER BY hours_since_fix DESC NULLS FIRST;