Strontium

SELECT `p`.`pressure`, `t`.`temperature`, `h`.`humidity`
  FROM (
    SELECT `DATA_SENSOR` AS `pressure`
      FROM `bmp_pressure`
      WHERE `DATESTAMP` <= :dateTime
      ORDER BY `DATESTAMP` DESC
      LIMIT 1
  ) AS `p`
  JOIN (
    SELECT `DATA_SENSOR` AS `temperature`
      FROM `bmp_temperature`
      WHERE `DATESTAMP` <= :dateTime
      ORDER BY `DATESTAMP` DESC
      LIMIT 1
  ) AS `t`
  JOIN (
    SELECT `DATA_SENSOR` AS `humidity`
      FROM `humidity`
      WHERE `DATESTAMP` <= :dateTime
      ORDER BY `DATESTAMP` DESC
      LIMIT 1
  ) AS `h`

SELECT `p`.`hour`, `p`.`pressure`, `t`.`temperature`, `h`.`humidity`
  FROM (
    SELECT HOUR(`DATESTAMP`) AS `hour`, `DATA_SENSOR` AS `pressure`
      FROM `bmp_pressure`
      WHERE `DATESTAMP` BETWEEN :date AND :date + INTERVAL 1 DAY
      GROUP BY HOUR(`DATESTAMP`)
  ) AS `p`
  JOIN (
    SELECT `DATA_SENSOR` AS `temperature`
      FROM `bmp_temperature`
      WHERE `DATESTAMP` BETWEEN :date AND :date + INTERVAL 1 DAY
      GROUP BY HOUR(`DATESTAMP`)
  ) AS `t` ON `t`.`hour` = `p`.`hour`
  JOIN (
    SELECT `DATA_SENSOR` AS `humidity`
      FROM `humidity`
      WHERE `DATESTAMP` BETWEEN :date AND :date + INTERVAL 1 DAY
      GROUP BY HOUR(`DATESTAMP`)
  ) AS `h` ON `h`.`hour` = `p`.`hour`