如何在 SQL 中从这个查询中只输出一个最大值？

Question

昨天Thomas 通过提供exactly the query I wanted 帮助了我很多。现在我需要它的一个变种，希望有人能帮助我。

我希望它只输出一行，即最大值 - 但它必须基于以下查询中的算法：

WITH Calendar AS (SELECT     CAST(@StartDate AS datetime) AS Date
                                          UNION ALL
                                          SELECT     DATEADD(d, 1, Date) AS Expr1
                                          FROM         Calendar AS Calendar_1
                                          WHERE     (DATEADD(d, 1, Date) < @EndDate))
    SELECT     C.Date, C2.Country, COALESCE (SUM(R.[Amount of people per day needed]), 0) AS [Allocated testers]
     FROM         Calendar AS C CROSS JOIN
                            Country AS C2 LEFT OUTER JOIN
                            Requests AS R ON C.Date BETWEEN R.[Start date] AND R.[End date] AND R.CountryID = C2.CountryID
     WHERE     (C2.Country = @Country)
     GROUP BY C.Date, C2.Country OPTION (MAXRECURSION 0)

上面的输出会是这样的：

Date            Country         Allocated testers
06/01/2010      Chile             3
06/02/2010      Chile             4
06/03/2010      Chile             0
06/04/2010      Chile             0
06/05/2010      Chile            19

但我现在需要的是

Allocated testers
           19

即 - 只有一列 - 一行 - 最大值本身...（对于（通过参数（已存在））选定的日期和国家期间）

Answer 1

使用order 和limit

ORDER BY 'people needed DESC' LIMIT 1 

编辑

因为 LIMIT 在 sql 中不存在

使用ORDER BY 和TOP

select TOP 1 .... ORDER BY 'people needed' DESC

Answer 2

WITH  Calendar
        AS (
             SELECT
              CAST(@StartDate AS datetime) AS Date
             UNION ALL
             SELECT
              DATEADD(d, 1, Date) AS Expr1
             FROM
              Calendar AS Calendar_1
             WHERE
              ( DATEADD(d, 1, Date) < @EndDate )
           )
SELECT TOP 1 *
FROM 
(           
  SELECT
    C.Date
   ,C2.Country
   ,COALESCE(SUM(R.[Amount of people per day needed]), 0) AS [Allocated testers]
  FROM
    Calendar AS C
    CROSS JOIN Country AS C2
    LEFT OUTER JOIN Requests AS R
      ON C.Date BETWEEN R.[Start date] AND R.[End date]
         AND R.CountryID = C2.CountryID
  WHERE
    ( C2.Country = @Country )
  GROUP BY
    C.Date
   ,C2.Country
OPTION
    ( MAXRECURSION 0 )
    ) lst
    ORDER BY lst.[Allocated testers] DESC

Answer 3

@Salil 回答中讨论的完整示例..

WITH Calendar AS (SELECT     CAST(@StartDate AS datetime) AS Date
                  UNION ALL
                  SELECT     DATEADD(d, 1, Date) AS Expr1
                  FROM         Calendar AS Calendar_1
                   WHERE     (DATEADD(d, 1, Date) < @EndDate))
SELECT  TOP 1   C.Date, C2.Country, COALESCE (SUM(R.[Amount of people per day needed]), 0) AS [Allocated testers]
FROM    Calendar AS C CROSS JOIN
        Country AS C2 LEFT OUTER JOIN
        Requests AS R ON C.Date BETWEEN R.[Start date] AND R.[End date] AND R.CountryID = C2.CountryID
WHERE     (C2.Country = @Country)
GROUP BY C.Date, C2.Country 
ORDER BY 3 DESC
OPTION (MAXRECURSION 0)

ORDER BY 3 表示按SELECT 语句中的第三个字段排序。因此，如果您删除前两个字段，请相应地进行更改。