MySQL 8.0

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CREATE TABLE sensor
    (`sensor` int, `service` int)
;
INSERT INTO sensor
    (`sensor`, `service`)
VALUES
    (1, 1),
    (2, 2)
;
CREATE TABLE equipment
    (`id` int, `equip` int, `sensor` int)
;
INSERT INTO equipment
    (`id`, `equip`, `sensor`)
VALUES
    (1, 8, 1),
    (2, 8, 1),
    (3, 8, 2),
    (4, 7, 2)
;
CREATE TABLE A
    (`id` int, `time` int, `temperature` varchar(4))
;
INSERT INTO A
    (`id`, `time`, `temperature`)
VALUES
    (1, 1027, '30'),
    (1, 1028, '30'),
    (1, 1029, NULL),
    (1, 1030, '60'),
    (1, 1101, '999')
;
CREATE TABLE B
    (`id` int, `time` int, `temperature` varchar(4))
;
INSERT INTO B
    (`id`, `time`, `temperature`)
VALUES
    (2, 1027, '40'),
    (2, 1029, '50'),
    (2, 1030, NULL),
    (2, 1031, '59')
;
SELECT t.time, MAX(A.temperature) AS A_temperature, MAX(B.temperature) AS B_temperature
FROM equipment e
JOIN sensor s ON s.sensor = e.sensor AND s.service = 1
JOIN (SELECT time FROM A UNION SELECT time FROM B ORDER BY time) t
LEFT JOIN A on A.id = e.id AND A.time = t.time
LEFT JOIN B on B.id = e.id AND B.time = t.time
WHERE t.time BETWEEN 1027 AND 1031
GROUP BY t.time
ORDER BY t.time


time
A_temperature
B_temperature


1027
30
40

1028
30
null

1029
null
50

1030
60
null

1031
null
59