Question

我对数据库查询知之甚少。例如，我有一个这样的表。

id | timestamp | lat   | lon
------------------------------
1  | 2016-04-06|-27.438|153.076
1  | 2016-04-03|-27.346|152.456
1  | 2016-04-04|-23.678|155.789
2  | 2016-04-04|-27.438|178.076
3  | 2016-04-04|-26.438|167.076
2  | 2016-04-05|-24.438|123.076

我用过：

SELECT * FROM table order by [Timestamp]DESC

按DESC顺序返回所有数据。但我需要从mssql查询中获取每个timestamp的最大id行。例如：

id | timestamp | lat   | lon
--------------------------------
1  | 2016-04-06|-27.438|153.076
2  | 2016-04-05|-24.438|123.076
3  | 2016-04-04|-26.438|167.076

Answer 1

使用ROW_NUMBER：

SELECT
    id, timestamp, lat, lon
FROM (
    SELECT *,
        rn = ROW_NUMBER() OVER(PARTITION BY id ORDER BY timestamp DESC)
    FROM yourTable
) t
WHERE rn = 1

Answer 2

使用row_number()按ID

获取最新时间戳

SELECT *
FROM
(
    SELECT *, R = ROW_NUMBER() OVER (PARTITION BY id ORDER BY timestamp DESC)
    FROM   yourtable
) D
WHERE R = 1

限制组后的行数

2 个答案: