MariaDB get counted values grouped by datetime for all possible dates - sql

Question

1.48 table which looks like this:
CREATE TABLE `history` (
`TIMESTAMP` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
`DEVICE` VARCHAR(64) NULL DEFAULT NULL COLLATE 'utf8_bin',
`TYPE` VARCHAR(64) NULL DEFAULT NULL COLLATE 'utf8_bin',
`EVENT` VARCHAR(512) NULL DEFAULT NULL COLLATE 'utf8_bin',
`READING` VARCHAR(64) NULL DEFAULT NULL COLLATE 'utf8_bin',
`VALUE` VARCHAR(128) NULL DEFAULT NULL COLLATE 'utf8_bin',
`UNIT` VARCHAR(32) NULL DEFAULT NULL COLLATE 'utf8_bin'
)
COLLATE='utf8_bin'
ENGINE=InnoDB
;
and some data which looks like this (only a small example of the available data)
INSERT INTO `history` (`TIMESTAMP`, `DEVICE`, `TYPE`, `EVENT`, `READING`, `VALUE`, `UNIT`) VALUES ('2023-01-04 21:16:06', 'DL_Motion', 'CUL_HM', 'state: motion', 'state', 'motion', '');
INSERT INTO `history` (`TIMESTAMP`, `DEVICE`, `TYPE`, `EVENT`, `READING`, `VALUE`, `UNIT`) VALUES ('2023-01-04 22:31:09', 'CD_Motion', 'CUL_HM', 'state: motion', 'state', 'motion', '');
INSERT INTO `history` (`TIMESTAMP`, `DEVICE`, `TYPE`, `EVENT`, `READING`, `VALUE`, `UNIT`) VALUES ('2023-01-04 23:24:58', 'AB_Motion', 'CUL_HM', 'state: motion', 'state', 'motion', '');
INSERT INTO `history` (`TIMESTAMP`, `DEVICE`, `TYPE`, `EVENT`, `READING`, `VALUE`, `UNIT`) VALUES ('2023-01-05 00:25:58', 'XY_Motion', 'CUL_HM', 'state: motion', 'state', 'motion', '');
INSERT INTO `history` (`TIMESTAMP`, `DEVICE`, `TYPE`, `EVENT`, `READING`, `VALUE`, `UNIT`) VALUES ('2023-01-05 01:27:58', 'XY_Motion', 'CUL_HM', 'state: motion', 'state', 'motion', '');
INSERT INTO `history` (`TIMESTAMP`, `DEVICE`, `TYPE`, `EVENT`, `READING`, `VALUE`, `UNIT`) VALUES ('2023-01-05 02:27:58', 'DL_Motion', 'CUL_HM', 'state: motion', 'state', 'motion', '');
INSERT INTO `history` (`TIMESTAMP`, `DEVICE`, `TYPE`, `EVENT`, `READING`, `VALUE`, `UNIT`) VALUES ('2023-01-05 02:29:02', 'DL_Motion', 'CUL_HM', 'state: motion', 'state', 'motion', '');
I want to have the amount of events grouped by date and hour for a dedicated device which works nice like this:
SELECT
DATE_FORMAT(TIMESTAMP,"%Y-%m-%d %H") AS ftimestamp,
COUNT(TIMESTAMP) AS amount
FROM
history
WHERE
DEVICE = 'DL_Motion'
AND READING = 'state'
AND VALUE = 'motion'
GROUP BY
YEAR(TIMESTAMP),MONTH(TIMESTAMP),DAY(TIMESTAMP),HOUR(TIMESTAMP);
and comes to the result:
ftimestamp
amount
2023-01-04 21
1
2023-01-05 02
2
For visualization purpose it would be great if I could get such a result:
ftimestamp
amount
2023-01-04 21
1
2023-01-04 22
0
2023-01-04 23
0
2023-01-04 00
0
2023-01-04 01
0
2023-01-05 02
2
So all possible dates and hours where no data available shall have a zero.
There are enough data in the table to generate the list of all possible dates and hours with the following select:
SELECT
DATE_FORMAT(TIMESTAMP,"%Y-%m-%d %H") AS ftimestamp
FROM
history
GROUP BY
YEAR(TIMESTAMP),MONTH(TIMESTAMP),DAY(TIMESTAMP),HOUR(TIMESTAMP);
I do not know how to combine this two request to come to the result I need.

Answer 1

If you have all dates available in the table, you can use conditional aggregation:
select date_format(timestamp, '%Y-%m-%d %H') as timestamp_hr,
sum(device = 'DL_Motion' and reading = 'state' and value = 'motion') as amount
from history
group by date_format(timestamp, '%Y-%m-%d %H')
The logic is to scan the whole table so we do get all available dates, and then to count the relevant rows only, using the conditional sum().
Note that I aligned the date expression in the select and group by clauses, which makes more sense in standard SQL.