Question

我在分组声明时遇到错误。这是我的代码

 DECLARE @avg_volume INT
 SELECT @avg_volume = ISNULL(AVG(Total_Volume), 0)
 FROM   ( SELECT    station_id ,
                    DATEPART(Year, date_time) AS YEAR ,
                    DATEPART(month, date_time) AS MONTH ,
                    CONVERT(DATE, date_time) AS DATE ,
                    DATENAME(weekday, date_time) AS weekday ,
                    SUM(volume) AS Total_volume
          FROM      rvtcs_data_aggregated_hourly
          GROUP BY  station_id ,
                    CONVERT(DATE, date_time) ,
                    DATEPART(month, date_time) ,
                    DATEPART(Year, date_time) ,
                    DATENAME(weekday, date_time)
        )
 GROUP BY station_id ,
        CONVERT(DATE, date_time) ,
        DATEPART(month, date_time) ,
        DATEPART(Year, date_time) ,
        DATENAME(weekday, date_time)
 ORDER BY DATEPART(Year, date_time) ,
        DATEPART(month, date_time) ,
        CONVERT(DATE, date_time)

 SELECT @avg_volume

我要做的是，通过一组条件（内部查询）从卷组中获取总和，这将得到结果

station_id  YEAR    MONTH   DATE            weekday Total_volume
7       2013    2   2013-02-21  Thursday    192
7       2013    2   2013-02-27  Wednesday   2699
7       2013    2   2013-02-28  Thursday    196
2       2013    3   2013-03-07  Thursday    192
7       2013    3   2013-03-07  Thursday    192

现在我想取平均值。任何帮助都会有所帮助。

我的表主表

station_id  date_time   volume

7   2013-02-21 00:00:00.000 96
7   2013-02-21 01:00:00.000 96
7   2013-02-27 00:00:00.000 356
7   2013-02-27 00:00:00.000 410
7   2013-02-27 00:00:00.000 471
7   2013-02-27 00:00:00.000 530
7   2013-02-27 00:00:00.000 338
7   2013-02-27 00:00:00.000 211
7   2013-02-27 00:00:00.000 159
7   2013-02-27 00:00:00.000 128
7   2013-02-27 00:00:00.000 96
7   2013-02-28 00:00:00.000 96
7   2013-02-28 01:00:00.000 100
7   2013-03-07 00:00:00.000 96
2   2013-03-07 00:00:00.000 96
2   2013-03-07 01:00:00.000 96
7   2013-03-07 01:00:00.000 96

期望的输出：

station id     year  month     weekday    average_volume
  7            2013     2      Thursday     194

Answer 1

您需要命名您的子查询：

DECLARE @avg_volume INT
 SELECT @avg_volume = ISNULL(AVG(Total_Volume), 0)
 FROM   ( SELECT    station_id ,
                    DATEPART(Year, date_time) AS YEAR ,
                    DATEPART(month, date_time) AS MONTH ,
                    CONVERT(DATE, date_time) AS DATE ,
                    DATENAME(weekday, date_time) AS weekday ,
                    SUM(volume) AS Total_volume
          FROM      rvtcs_data_aggregated_hourly
          GROUP BY  station_id ,
                    CONVERT(DATE, date_time) ,
                    DATEPART(month, date_time) ,
                    DATEPART(Year, date_time) ,
                    DATENAME(weekday, date_time)

        ) AnyNameYouLikeButYouHaveToGiveOne --<-- Here

 GROUP BY station_id ,
        CONVERT(DATE, date_time) ,
        DATEPART(month, date_time) ,
        DATEPART(Year, date_time) ,
        DATENAME(weekday, date_time)
 ORDER BY DATEPART(Year, date_time) ,
        DATEPART(month, date_time) ,
        CONVERT(DATE, date_time)

 SELECT @avg_volume

Answer 2

您的查询中几乎没有基本问题。您总结并找出基于月份日ETC的平均值。我没有看到任何过滤器，一年或一个月或站ID。所以我假设你的最终选择查询中会有多行，而你正在选择一个变量。所以你可能只得到变量中第一行/最后一行的值（当然取决于排序）。你必须在这里对查询做一些修改。

此查询是否为您提供了正确的输出？

SELECT  ISNULL(AVG(Total_volume), 0)
FROM    ( SELECT    station_id ,
                    DATEPART(year, date_time) AS YEAR ,
                    DATEPART(month, date_time) AS MONTH ,
                    CONVERT(DATE, date_time) AS DATE ,
                    DATENAME(weekday, date_time) AS weekday ,
                    SUM(volume) AS Total_volume
          FROM      rvtcs_data_aggregated_hourly
          GROUP BY  station_id ,
                    CONVERT(DATE, date_time) ,
                    DATEPART(month, date_time) ,
                    DATEPART(year, date_time) ,
                    DATENAME(weekday, date_time)
          ORDER BY  DATEPART(year, date_time) ,
                    DATEPART(month, date_time) ,
                    CONVERT(DATE, date_time)
        ) T;

Answer 3

根据您的目的，您不需要进行第二次显式聚合或order by。只取平均值：

DECLARE @avg_volume INT
SELECT  @avg_volume = ISNULL(AVG(Total_Volume), 0)
FROM    ( SELECT    station_id ,
                    DATEPART(Year, date_time) AS "YEAR" ,
                    DATEPART(month, date_time) AS "MONTH" ,
                    CONVERT(DATE, date_time) AS "date" ,
                    DATENAME(weekday, date_time) AS weekday ,
                    SUM(volume) AS Total_volume
          FROM      rvtcs_data_aggregated_hourly
          GROUP BY  station_id ,
                    CONVERT(DATE, date_time) ,
                    DATEPART(month, date_time) ,
                    DATEPART(Year, date_time) ,
                    DATENAME(weekday, date_time)
        ) t;

您的具体错误是因为您在子查询中没有别名（好吧，关键字group不算作别名）。

你的一些专栏命名为关键字，所以我引用了这些。这些单词的列表是here。

实际上，在编写这样的查询时，您不需要在select中包含所有列，所以您也可以这样做：

DECLARE @avg_volume INT
SELECT  @avg_volume = ISNULL(AVG(Total_Volume), 0)
FROM    ( SELECT    SUM(volume) AS Total_volume
          FROM      rvtcs_data_aggregated_hourly
          GROUP BY  station_id ,
                    CONVERT(DATE, date_time) ,
                    DATEPART(month, date_time) ,
                    DATEPART(Year, date_time) ,
                    DATENAME(weekday, date_time)
        ) t;

关键字'GROUP'IN SQL附近的语法不正确

3 个答案: