CREATE TABLE `measurements` (
 `row_id` int(11) NOT NULL AUTO_INCREMENT,
 `process_name` varchar(100) COLLATE utf8_bin NOT NULL,
 `process_id` int(11) NOT NULL,
 `process_group_id` tinyint(4) NOT NULL,
 `measurement_1` float NOT NULL,
 `measurement_2` float NOT NULL,
 `measurement_3` float NOT NULL,
 `measurement_4` float NOT NULL,
 `start_timestamp` int(11) NOT NULL,
 `end_timestamp` int(11) NOT NULL,
 PRIMARY KEY (`row_id`),
 KEY `process_group_id` (`process_group_id`,`start_timestamp`,`end_timestamp`),
 KEY `process_id` (`process_id`)
) ENGINE=InnoDB AUTO_INCREMENT=7294932 DEFAULT CHARSET=utf8 COLLATE=utf8_bin

SELECT  SUM(measurement_1), SUM(measurement_2), SUM(measurement_3),
        SUM(measurement_4)
    FROM  measurements
    WHERE  process_group_id = 5
      AND  1431388800 BETWEEN start_timestamp AND end_timestamp

SELECT  process_group_id, SUM(measurement_1), SUM(measurement_2),
        SUM(measurement_3), SUM(measurement_4)
    FROM  measurements
    WHERE  process_group_id = 5
      AND  1431388800 BETWEEN start_timestamp AND end_timestamp
    ORDER BY  process_group_id ASC

AND  1431388800 BETWEEN start_timestamp AND end_timestamp

AND  start_timestamp <= 1431388800
AND  end_timestamp   >= 1431388800

CREATE TABLE ByMinute (
    process_group_id ...
    ts TIMESTAMP NOT NULL, -- rounded to the minute
    sum_1 FLOAT  -- see below
    sum_2 ...,
    PRIMARY KEY(process_group_id, ts)
);

SELECT  sum_1, sum_2, sum_3, sum_4
    FROM  ByMinute
    WHERE  process_group_id = 5
      AND  ts = somehow round 1431388800 to a minute