SQL關鍵字“ GROUP”附近的語法不正確

Question

我在對語句進行分組時遇到錯誤。 這是我的代碼

 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，通過一組條件（內部查詢）從卷組中獲取總和，其結果為

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

現在我想取其平均值。 任何幫助都會有所幫助。

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

所需輸出：

station id     year  month     weekday    average_volume
  7            2013     2      Thursday     194

Answer 1

您需要命名子查詢：

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

您的查詢中幾乎沒有基本問題。 您正在匯總，並且根據月份年份日期ETC求平均值。 我沒有看到任何過濾器，例如年份或月份或站點ID。 因此，我認為最終選擇查詢中將有多於一行，並且您正在選擇一個變量。 因此，您可能只能從變量的第一行/最后一行獲取值（當然，取決於順序）。您必須在此處對查詢進行一些修改。

該查詢是否為您提供正確的輸出？

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

根據您要執行的操作，您無需進行第二次顯式聚合或order by 。 僅取平均值：

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;

您的特定錯誤是因為您在子查詢上沒有別名（嗯，關鍵字group不算作別名）。

您的某些專欄為關鍵詞命名，因此我引用了這些關鍵詞。 這些單詞的清單在這里 。

實際上，當編寫這樣的查詢時，您不需要在select包括所有列，因此您還可以這樣做：

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;