在每个 window - MariaDB/MySQL 中查找最新记录

Question

在 MariaDb 10.3 中，如何为每个 window（或分区，我对这里的术语不太清楚）找到最新的（基于时间戳）行？

考虑以下 table 和数据

ItemID	Itemname	Value	Timestamp
1	A	22	2021-12-22 20:01:00
1	A	2	2021-12-22 15:09:44
1	A	3	2021-12-22 14:39:49
2	B	54	2021-12-22 12:46:37
2	B	23	2021-12-22 12:17:52
2	B	43	2021-12-22 11:19:11
1	A	23	2021-12-22 04:00:58
1	A	53	2021-12-22 03:00:58
3	C	21	2021-12-21 04:00:58
2	B	74	2021-12-21 04:06:58
2	B	36	2021-12-21 04:06:09
1	A	34	2021-12-21 03:08:09

期望的输出

ItemID	ItemName	Value	Timestamp
1	A	22	2021-12-22 20:01:00
2	B	54	2021-12-22 12:46:37
1	A	23	2021-12-22 04:00:58
3	C	21	2021-12-21 04:00:58
2	B	74	2021-12-21 04:06:58
1	A	34	2021-12-21 03:08:09

Answer 1

以下查询生成预期结果

WITH ordered AS (
  SELECT 
    *, 
    LAG(`ItemID`) OVER (ORDER BY `Timestamp` DESC) AS LastItem
  FROM dataset
)
SELECT `ItemID`, `ItemName`, `Value`, `Timestamp`
FROM ordered
WHERE `ItemID` <> `LastItem` OR `LastItem` IS NULL
ORDER BY `Timestamp` DESC

demo

在每个 window - MariaDB/MySQL 中查找最新记录

Finding the latest record in each window - MariaDB/MySQL

mysql

mariadb