MySQL 5.5

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CREATE TABLE `scantech_data` (
`scdate` varchar(20),
`value` float
);

INSERT INTO `scantech_data` VALUES ('2021-11-10 17:00:00',1943.98);
INSERT INTO `scantech_data` VALUES ('2021-11-10 17:00:18',1957.13);
INSERT INTO `scantech_data` VALUES ('2021-11-10 17:00:36',1953.94);
INSERT INTO `scantech_data` VALUES ('2021-11-10 17:00:54',1946.28);
INSERT INTO `scantech_data` VALUES ('2021-11-10 17:01:12',1960.29);
INSERT INTO `scantech_data` VALUES ('2021-11-10 17:01:29',1950.39);
INSERT INTO `scantech_data` VALUES ('2021-11-10 17:01:47',1942.62);
INSERT INTO `scantech_data` VALUES ('2021-11-10 17:02:05',1954.64);
INSERT INTO `scantech_data` VALUES ('2021-11-10 17:02:23',1958.21);
INSERT INTO `scantech_data` VALUES ('2021-11-10 17:02:41',1950.26);
INSERT INTO `scantech_data` VALUES ('2021-11-10 17:02:58',1945.33);
INSERT INTO `scantech_data` VALUES ('2021-11-10 17:03:16',1960.35);
-- 額外加入
INSERT INTO `scantech_data` VALUES ('2021-11-10 17:04:33',NULL);

SELECT *
FROM scantech_data
ORDER BY scdate

scdate	value
2021-11-10 17:00:00	1943.98
2021-11-10 17:00:18	1957.13
2021-11-10 17:00:36	1953.94
2021-11-10 17:00:54	1946.28
2021-11-10 17:01:12	1960.29
2021-11-10 17:01:29	1950.39
2021-11-10 17:01:47	1942.62
2021-11-10 17:02:05	1954.64
2021-11-10 17:02:23	1958.21
2021-11-10 17:02:41	1950.26
2021-11-10 17:02:58	1945.33
2021-11-10 17:03:16	1960.35
2021-11-10 17:04:33	null

scdate	value	avg_v
2021-11-10 17:00:00	1943.98	1951.68
2021-11-10 17:00:18	1957.13	1952.45
2021-11-10 17:00:36	1953.94	1953.50
2021-11-10 17:00:54	1946.28	1952.32
2021-11-10 17:01:12	1960.29	1951.10
2021-11-10 17:01:29	1950.39	1949.22
2021-11-10 17:01:47	1942.62	1951.82
2021-11-10 17:02:05	1954.64	1954.37
2021-11-10 17:02:23	1958.21	1951.27
2021-11-10 17:02:41	1950.26	1951.98
2021-11-10 17:02:58	1945.33	1952.84
2021-11-10 17:03:16	1960.35	1960.35
2021-11-10 17:04:33	null	null