SQL选择:如何从有序数据集返回连续值的计数

Question

以下是我在SQL Server 2008数据库中拥有的表的子集.

我试图输出Serial Number时,LID用连续的最大计LID值,而实际计数.重要的是要注意表格Last Updated Date按降序值排序(这个条件很关键).它可以按升序或降序分组Serial Number或排序Serial Number......任何更有效和有意义的东西.

这是数据的样子:

[Serial Number]  [LID]   [Last Updated Date]
--------------------------------------    
123456            AAA     2012-09-24
123456            AAA     2012-09-23
123456            AAA     2012-09-22
123456            AAA     2012-09-21
123456            BBB     2012-09-20
123456            BBB     2012-09-19
123456            AAA     2012-09-18
123456            AAA     2012-09-17
123456            AAA     2012-09-16
234567            BBB     2012-09-24
234567            BBB     2012-09-23
234567            AAA     2012-09-22

表的所​​需输出是:

[Serial Number]     [LID]     [LID Count]
-------------------------------------------    
123456            AAA     4
234567            BBB     2

我很茫然.我试过用了

ROW_NUMBER() OVER(PARTITION BY [Service Tag], [LID]
                  ORDER BY [Last Updated Date] DESC) 

但所有这一切都是打破我的降序日期顺序,我最终得到的计数和日期范围内发生最多的LID.

在此先感谢您提供的任何帮助!

最好的祝福,

VP

Answer 1

看看下面的例子

SQL 小提琴演示

DECLARE @Table TABLE(
        [Serial Number] INT,
        [LID] VARCHAR(50),
        [Last Updated Date] DATETIME
)

INSERT INTO @Table SELECT 123456,'AAA','2012-09-24'
INSERT INTO @Table SELECT 123456,'AAA','2012-09-23'
INSERT INTO @Table SELECT 123456,'AAA','2012-09-22'
INSERT INTO @Table SELECT 123456,'AAA','2012-09-21'
INSERT INTO @Table SELECT 123456,'BBB','2012-09-20'
INSERT INTO @Table SELECT 123456,'BBB','2012-09-19'
INSERT INTO @Table SELECT 123456,'AAA','2012-09-18'
INSERT INTO @Table SELECT 123456,'AAA','2012-09-17'
INSERT INTO @Table SELECT 123456,'AAA','2012-09-16'
INSERT INTO @Table SELECT 234567,'BBB','2012-09-24'
INSERT INTO @Table SELECT 234567,'BBB','2012-09-23'
INSERT INTO @Table SELECT 234567,'AAA','2012-09-22'

;WITH Vals AS (
        SELECT  *,
                ROW_NUMBER() OVER(ORDER BY [Serial Number],[Last Updated Date] DESC) ROWID
        FROM    @Table
)
, ValsNext AS (
        SELECT  v.[Serial Number],
                v.LID,
                v.[Last Updated Date],
                v.ROWID,
                MIN(vn.ROWID) NextRowID
        FROM    Vals v LEFT JOIN
                Vals vN ON  v.[Serial Number] = vn.[Serial Number]
                        AND v.LID != vn.LID
                        AND v.ROWID < vn.ROWID
        GROUP BY    v.[Serial Number],
                    v.LID,
                    v.[Last Updated Date],
                    v.ROWID
)
, ValDiffs AS (
        SELECT  vn.[Serial Number],
                vn.LID,
                vn. NextRowID - vn.ROWID Consecutive
        FROM    ValsNext vn
)
, Serials AS (
        SELECT  [Serial Number],
                MAX(Consecutive) MaxConsecutive
        FROM    ValDiffs
        GROUP BY    [Serial Number]
)
SELECT  vd.*
FROM    Serials s INNER JOIN
        ValDiffs vd ON  s.[Serial Number] = vd.[Serial Number]
                    AND s.MaxConsecutive = vd.Consecutive