FOR XML PATH 应用及其反向分解

数据库环境：SQL SERVER 2005

　　我们实现将同一组的数据内容合并到一行的时候，可以通过FOR XML PATH来实现。

有数据如图1，要实现图2的效果

            

1.图1到图2的FOR XML PATH实现

　　网上有很多介绍FOR XML的方法，这里不再细说，感兴趣的朋友可以去查询一下它的用法。

--数据准备
;WITH    x0
          AS ( SELECT   1 AS id ,
                        '' AS ty
               UNION ALL
               SELECT   1 AS id ,
                        '' AS ty
               UNION ALL
               SELECT   2 AS id ,
                        '' AS ty
               UNION ALL
               SELECT   3 AS id ,
                        '' AS ty
               UNION ALL
               SELECT   3 AS id ,
                        '' AS ty
               UNION ALL
               SELECT   4 AS id ,
                        '' AS ty
               UNION ALL
               SELECT   4 AS id ,
                        '' AS ty
               UNION ALL
               SELECT   4 AS id ,
                        '' AS ty
             )
    /*实现*/
    SELECT  id ,
            STUFF(ty, 1, 1, '') AS ty
    FROM    ( SELECT    id ,
                        ( SELECT    ',' + x2.ty
                          FROM      x0 x2
                          WHERE     x2.id = x1.id
                        FOR
                          XML PATH('')
                        ) AS ty
              FROM      x0 x1
              GROUP BY  id
            ) t

2.图2到图1的递归实现

　　从图2到图1，实现的方法不止递归一种方法，各位可以试着用其它方法解决。

/*准备数据*/
WITH    x0
          AS ( SELECT   1 AS id ,
                        '001,002' AS ty
               UNION ALL
               SELECT   2 AS id ,
                        '' AS ty
               UNION ALL
               SELECT   3 AS id ,
                        '004,1234' AS ty
               UNION ALL
               SELECT   4 AS id ,
                        '01,005,006' AS ty
             ),
        x1 ( id, ty1, ty2 )
          AS ( SELECT   id ,
                        CASE WHEN CHARINDEX(',', ty, 1) > 0
                             THEN CONVERT(VARCHAR(10), LEFT(ty,
                                                            CHARINDEX(',', ty,
                                                              1) - 1))
                             ELSE ty
                        END AS ty1 ,--本次拆分字符
                        CASE WHEN CHARINDEX(',', ty, 1) > 0 THEN
                             STUFF(ty + ',', 1, CHARINDEX(',', ty), '')
                             ELSE NULL
                        END AS ty2--待拆分字符串
               FROM     x0
               UNION ALL
               SELECT   id ,
                        CONVERT(VARCHAR(10), LEFT(ty2,
                                                  NULLIF(CHARINDEX(',', ty2, 1),
                                                         0) - 1)) AS ty1 ,--本次拆分字符
                        STUFF(ty2, 1, CHARINDEX(',', ty2), '') AS ty2--待拆分字符串
               FROM     x1
               WHERE    CHARINDEX(',', ty2, 1) > 0
             )
    SELECT  id,ty1 AS ty
    FROM    x1 ORDER BY id