使用 GROUP BY 时选择其他字段

Question

我使用的是 MSSQL 2008 R2，遇到以下情况：

通过以下查询，我将获得我期望的数据（每个日期的 max 和 min 速度）。 CAST(m.date as DATE) 删除了我的datetime 的时间部分

SELECT CAST(d.date as DATE) as date,
       MAX(d.speed) AS maxSpeed,
       AVG(d.speed) AS avgSpeed
  FROM Driver as d
 WHERE d.date between '2014-01-01 09:00:00.491' and
       '2014-03-11 17:00:00.491'
 GROUP BY CAST(d.date as DATE)
 ORDER BY date DESC

我的问题是，我还想从 d 中选择一些其他字段（例如用户 ID、用户名等）。如果我修改查询以包含其他字段，如下所示：

SELECT CAST(d.date as DATE) as date,
       MAX(d.speed) AS maxSpeed,
       AVG(d.speed) AS avgSpeed,
       d.userId
  FROM Driver as d
 WHERE d.date between '2014-01-01 09:00:00.491' and
       '2014-03-11 17:00:00.491'
 GROUP BY CAST(d.date as DATE)
 ORDER BY date DESC

我收到此错误：

d.userId is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

因此，我将d.userId 添加到GROUP BY 子句中，我的数据当然会发生变化，现在每个日期将包含多个条目。

所以，我的问题是如何选择其他字段，同时仍保留我想要的原始数据（每个唯一日期的 min 和 max）？

Answer 1

如果您想从Driver 中选择行以及speed 的max() 和avg() 值，请使用窗口函数：

SELECT d.*, CAST(d.date as DATE) as date,
       MAX(d.speed) OVER (PARTITION BY CAST(d.date as DATE)) AS maxSpeed,
       AVG(d.speed) OVER (PARTITION BY CAST(d.date as date)) AS avgSpeed
FROM Driver as d
WHERE d.date between '2014-01-01 09:00:00.491' and '2014-03-11 17:00:00.491'
ORDER BY date DESC;

编辑：

如果您希望每位司机每天一排，请使用简单的group by：

SELECT d.userId, CAST(d.date as DATE) as date,
       MAX(d.speed) as maxSpeed, AVG(d.speed) as avgSpeed
FROM Driver as d
WHERE d.date between '2014-01-01 09:00:00.491' and '2014-03-11 17:00:00.491'
GROUP BY d.userId, CAST(d.date as DATE) 
ORDER BY date DESC;

如果要添加其他列，则需要将它们同时添加到 select 和 group by。