Question

我对编写SQL比较陌生。我有一个要求，我必须按原样显示前5条记录，并将其余记录合并为1条记录并将其作为第6条记录追加。我知道前5个选择了前5个记录，但我发现很难将逻辑组合起来合并其余记录并将其附加到结果集的底部。

weekof          sales    year    weekno
-------------------------------------------------------------
07/01 - 07/07   2   2012    26  
07/08 - 07/14   2   2012    27  
07/29 - 08/04   1   2012    30  
08/05 - 08/11   1   2012    31  
08/12 - 08/18   32  2012    32  
08/26 - 09/01   2   2012    34  
09/02 - 09/08   8   2012    35  
09/09 - 09/15   46  2012    36   
09/16 - 09/22   26  2012    37

我希望将其显示为

weekof          sales
----------------------
09/16 - 09/22   26  
09/09 - 09/15   46  
09/02 - 09/08   8   
08/26 - 09/01   2   
08/12 - 08/18   32  
07/01 - 08/11   6

Answer 1

除非weekof跨越多年，否则这将以正确的顺序获取您想要的数据和：

;WITH x AS 
(
  SELECT weekof, sales, 
    rn = ROW_NUMBER() OVER (ORDER BY [year] DESC, weekno DESC) 
  FROM dbo.table_name
)
SELECT weekof, sales FROM x WHERE rn <= 5
UNION ALL
SELECT MIN(LEFT(weekof, 5)) + ' - ' + MAX(RIGHT(weekof, 5)), SUM(sales)
FROM x WHERE rn > 5    
ORDER BY weekof DESC;

当返回的行跨越一年时，您可能还必须返回rn（并且只是在表示层忽略它）：

;WITH x AS 
(
  SELECT weekof, sales, 
    rn = ROW_NUMBER() OVER (ORDER BY [year] DESC, weekno DESC) 
  FROM dbo.table_name
)
SELECT weekof, sales, rn FROM x WHERE rn <= 5
UNION ALL
SELECT MIN(LEFT(weekof, 5)) + ' - ' + MAX(RIGHT(weekof, 5)), SUM(sales), rn = 6 
FROM x WHERE rn > 5
ORDER BY rn;

Answer 2

这是一个替代版本，即使在跨越年份时也以正确的顺序显示，并且需要单次扫描而不是两次（仅当数据量很大时才重要）。它将在SQL 2005及更高版本中运行：

WITH Sales AS (
   SELECT
      Seq = Row_Number() OVER (ORDER BY S.yr DESC, S.weekno DESC),
      *
   FROM dbo.SalesByWeek S
)
SELECT
   weekof =
      Substring(Min(Convert(varchar(11), S.yr) + Left(S.weekof, 5)), 5, 5)
      + ' - '
      + Substring(Max(Convert(varchar(11), S.yr) + Right(S.weekof, 5)), 5, 5),
   sales = Sum(S.sales)
FROM
   Sales S
   OUTER APPLY (SELECT S.Seq WHERE S.Seq <= 5) G
GROUP BY G.Seq   
ORDER BY Coalesce(G.Seq, 2147483647)
;

还有一个查询可能对非常大的数据集执行得更好，因为它不计算行号（而是使用TOP一次）。但是，如果没有真正的数据和性能测试，这都是理论上的：

SELECT
   weekof =
      Substring(Min(Convert(varchar(11), S.yr) + Left(S.weekof, 5)), 5, 5)
      + ' - '
      + Substring(Max(Convert(varchar(11), S.yr) + Right(S.weekof, 5)), 5, 5),
   sales = Sum(S.sales)
FROM
   dbo.SalesByWeek S
   LEFT JOIN (
      SELECT TOP 5 *
      FROM dbo.SalesByWeek
      ORDER BY yr DESC, weekno DESC
   ) G ON S.yr = G.yr AND S.weekno = G.weekno
GROUP BY G.yr, G.weekno
ORDER BY Coalesce(G.yr, 9999), G.weekno
;

最终，我真的不喜欢字符串操作来取出日期范围。如果表格将MinDate和MaxDate作为单独的列，然后为它们创建标签会更简单，那会更好。

显示前n个记录并合并其余行

2 个答案: