树形查询扩展

数据库环境：SQL SERVER 2005

　　有一层次表的数据如下图1，要实现图2的效果，即将层次结构的路径按行显示，

第一列显示的是叶子节点，后面则是分枝节点，最后是根节点。

        

　　要解决的问题：

　　1.递归实现树形查询

      2.从根节点到叶子节点编成一组

　　3.动态行转列

　　好了，我们依次来解决这些问题。

　　0.建表，导入基础数据

WITH x0 AS(
SELECT 1 AS id,'1xx' AS name,2 AS fatherID UNION ALL
SELECT 2 AS id,'2xx' AS name,3 AS fatherID UNION ALL
SELECT 3 AS id,'3xx' AS name,0 AS fatherID UNION ALL
SELECT 4 AS id,'4xx' AS name,3 AS fatherID UNION ALL
SELECT 0 AS id,'0xx' AS name,NULL AS fatherID)

SELECT * INTO #t FROM x0

　　1.递归分组

　　分组的组号依据叶子节点的id而定，从叶子节点追溯到根节点，它们属于同一组。

/*递归实现层次查询*/
WITH    x0 ( id, name, fatherID, way, level )
          AS ( SELECT   id ,
                        name ,
                        fatherID ,
                        CONVERT(VARCHAR(50), CAST(id AS VARCHAR(2))) AS way ,
                        id AS level
               FROM     #t t1
               /*从叶子节点开始递归*/
               WHERE    NOT EXISTS ( SELECT NULL
                                     FROM   #t t2
                                     WHERE  t2.fatherID = t1.id )
               UNION ALL
               SELECT   t1.id ,
                        t1.name ,
                        t1.fatherID ,
                        CONVERT(VARCHAR(50), CAST(t1.id AS VARCHAR(2)) + '->'
                        + t2.way) AS way ,--路径
                        t2.level--组别
               FROM     #t t1 ,
                        x0 t2
               WHERE    t1.id = t2.fatherID
             )

　　层次查询的结果如图：

　　2.动态行转列实现

　　有了组号，我们则根据同一组号的数据转到一行上展示。这里需要注意行转列的展示顺序，

排在前面的是子节点，后面是父节点。关于动态行转列的实现，可参考我前面的博客 将部分相同的多行记录转成一行多列。

SELECT  id ,
            name ,
            level ,
            ROW_NUMBER() OVER ( PARTITION BY level ORDER BY LEN(way) ) AS rn--节点的展示序号
    INTO    #t1
    FROM    x0
    
DECLARE @sql NVARCHAR(MAX);   
SET @sql = N'';
SELECT  @sql = @sql + ',max(case rn when ' + CAST(tt.rn AS VARCHAR)
        + ' then id end) ' + CASE WHEN rn = 1 THEN +'id'
                                  ELSE 'faterID'
                             END + ',max(case rn when '
        + CAST(tt.rn AS VARCHAR) + ' then name end) '
        + CASE WHEN rn = 1 THEN +'name'
               ELSE 'faterName'
          END
FROM    ( SELECT DISTINCT
                    rn
          FROM      #t1
        ) tt
ORDER BY rn;

SET @sql = N'select level' + @sql + ' from #t1 group by level';
EXEC(@sql);

（本文完）