查找字段连续相同的最大值

数据库环境：SQL SERVER 2008R2

有基础数据如图1，要求取出id字段连续值为一组的cn最大值，即图2中红框圈中的部分。

     

先导入基础数据

WITH    x0

          AS ( SELECT   1 AS id ,

                        100 AS cn

               UNION ALL

               SELECT   1 AS id ,

                        200 AS cn

               UNION ALL

               SELECT   1 AS id ,

                        300 AS cn

               UNION ALL

               SELECT   2 AS id ,

                        400 AS cn

               UNION ALL

               SELECT   2 AS id ,

                        200 AS cn

               UNION ALL

               SELECT   1 AS id ,

                        600 AS cn

               UNION ALL

               SELECT   1 AS id ,

                        700 AS cn

             )

             

    SELECT * INTO #tt FROM x0

实现的步骤分两步，第一步是将连续id分组，则提供的基础数据可以分成3组。

--添加一列自增数量，并插入到新表#t

SELECT IDENTITY(int,1,1) AS rowid,* INTO #t FROM #tt

--将id连续数据分组

WITH    t0 ( rowid, id, cn, groupid )

          AS ( SELECT   rowid ,

                        id ,

                        cn ,

                        1 AS groupid

               FROM     #t

               WHERE    rowid = 1

               UNION ALL

               SELECT   a.rowid ,

                        a.id ,

                        a.cn ,

                        CASE WHEN a.id = b.id THEN b.groupid

                             ELSE b.groupid + 1

                        END groupid

               FROM     #t a

                        INNER JOIN t0 b ON b.rowid = a.rowid - 1

             )

分组后的数据如下图

第二步，按照groupid字段分组，并找出组中最大的cn值。

SELECT  id ,

            cn

    FROM    ( SELECT    id ,

                        cn ,

                        MAX(cn) OVER ( PARTITION BY groupid ) AS mcn

              FROM      t0

            ) t

    WHERE   cn = mcn

最终结果如图