Fill in the missing hours with insert and recursive left join - mysql

Question

I have a table with temperatures.
Sometimes the message was not received and the information is missing.
I need to fill the missing rows with NULL for every hour.
CREATE TABLE temp_total(
id int(6) NOT NULL PRIMARY KEY,
stamp timestamp NOT NULL,
room_temp decimal(3,1) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
ALTER TABLE temp_total
ADD UNIQUE KEY stamp(stamp),
MODIFY id int(6) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=1;
INSERT INTO temp_total(stamp, room_temp) VALUES
('2019-07-21 19:00:00', '23.4'),
('2019-07-21 22:00:00', '22.7'),
('2019-07-23 02:00:00', '22.5'),
('2019-07-23 06:00:00', '22.4');
The expected result is an array of 36 rows.
I found this query to work fine.
SELECT stamp INTO #deb FROM temp_total ORDER BY stamp ASC LIMIT 1;
SELECT stamp INTO #fin FROM temp_total ORDER BY stamp DESC LIMIT 1;
WITH RECURSIVE all_hours(dt) AS (
SELECT #deb dt
UNION ALL
SELECT dt + INTERVAL 1 HOUR FROM all_hours
WHERE dt + INTERVAL 1 HOUR < #fin + INTERVAL 1 HOUR
)
-- INSERT IGNORE INTO temp_total(stamp, room_temp)
SELECT d.dt stamp, t.room_temp
FROM all_hours d
LEFT JOIN temp_total t ON t.stamp = d.dt
ORDER BY d.dt;
I want to use the result of SELECT with INSERT but I get this message:
#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'INSERT INTO temp_total(stamp, room_temp)
SELECT d.dt stamp, t.room_temp
...' at line 7
When I uncomment the line.
DbFiddle

Answer 1

You are almost there. With a small change in the syntax the query works as expected:
INSERT IGNORE INTO temp_total(stamp, room_temp)
WITH RECURSIVE all_hours(dt) AS (
SELECT #deb dt
UNION ALL
SELECT dt + INTERVAL 1 HOUR FROM all_hours
WHERE dt + INTERVAL 1 HOUR < #fin + INTERVAL 1 HOUR
)
SELECT d.dt stamp, t.room_temp
FROM all_hours d
LEFT JOIN temp_total t ON t.stamp = d.dt
ORDER BY d.dt;
See running example at db<>fiddle.