SQL关键字“ GROUP”附近的语法不正确

Question

我在对语句进行分组时遇到错误。 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

我想做的是，通过一组条件（内部查询）从卷组中获取总和，其结果为

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

现在我想取其平均值。 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

所需输出：

station id     year  month     weekday    average_volume
  7            2013     2      Thursday     194

Answer 1

您需要命名子查询：

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。 您正在汇总，并且根据月份年份日期ETC求平均值。 我没有看到任何过滤器，例如年份或月份或站点ID。 因此，我认为最终选择查询中将有多于一行，并且您正在选择一个变量。 因此，您可能只能从变量的第一行/最后一行获取值（当然，取决于顺序）。您必须在此处对查询进行一些修改。

该查询是否为您提供正确的输出？

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

根据您要执行的操作，您无需进行第二次显式聚合或order by 。 仅取平均值：

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;

您的特定错误是因为您在子查询上没有别名（嗯，关键字group不算作别名）。

您的某些专栏为关键词命名，因此我引用了这些关键词。 这些单词的清单在这里 。

实际上，当编写这样的查询时，您不需要在select包括所有列，因此您还可以这样做：

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;