MySQL 8.0

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CREATE TABLE outside_temp (
  `savetime` DATETIME,
  `weatherdata` FLOAT,
  `newflag` INTEGER
);

INSERT INTO outside_temp
  (`savetime`, `weatherdata`, `newflag`)
VALUES
  ('2020-01-31 01:10:00', '8.9', '1'),
  ('2020-01-31 03:25:00', '8.9', '1'),
  ('2020-01-31 05:40:00', '9.1', '1'),
  ('2020-01-31 00:10:00', '8.8', '1'),
  ('2020-01-31 04:25:00', '9.3', '1'),
  ('2020-01-31 00:55:00', '9', '1'),
  ('2020-01-31 01:25:00', '8.9', '1'),
  ('2020-01-31 00:25:00', '8.9', '1'),
  ('2020-01-31 04:10:00', '9.3', '1');
CREATE TABLE rainfall (
  `savetime` VARCHAR(34),
  `raincounter` INTEGER,
  `counteramount` INTEGER,
  `israining` INTEGER,
  `newflag` INTEGER
);

INSERT INTO rainfall
  (`savetime`, `raincounter`, `counteramount`, `israining`, `newflag`)
VALUES
  ('2020-01-31 09:10:00', '2016', '37290', '0', '1'),
  ('2020-01-31 16:56:00', '2016', '37290', '0', '1'),
  ('2020-01-31 07:40:00', '2016', '37290', '0', '1'),
  ('2020-01-31 05:10:00', '2016', '37290', '0', '1'),
  ('2020-01-31 11:11:00', '2016', '37290', '0', '1'),
  ('2020-01-31 15:11:00', '2016', '37290', '0', '1'),
  ('2020-01-31 20:56:00', '2016', '37290', '0', '1'),
  ('2020-01-31 11:41:00', '2016', '37290', '0', '1'),
  ('2020-01-31 08:55:00', '2016', '37290', '0', '1'),
  ('2020-01-31 15:41:00', '2016', '37290', '0', '1'),
  ('2020-01-31 12:11:00', '2016', '37290', '0', '1');
SELECT 
    savetime_temp
    ,AVG_temp
    ,rainc
FROM
(SELECT 
    DATE(savetime) DAY_temp
,MIN(savetime) savetime_temp
    ,AVG(weatherdata) AS AVG_temp
FROM
    outside_temp
WHERE
    savetime >= DATE_SUB(CURDATE(), INTERVAL 360 DAY)
GROUP BY  DAte(savetime)) t1 
INNER JOIN
(SELECT 
    DATE(savetime) DAY_rainc
    ,MIN(savetime) savetime_rainc
    ,(MAX(counteramount) - MIN(counteramount)) * 295 / 1000 AS rainc

FROM
    rainfall 
 GROUP BY DAte(savetime)) t2
 ON t1.DAY_temp = t2.DAY_rainc


savetime_temp
AVG_temp
rainc


2020-01-31 00:10:00
9.011111047532824
0.0000