SQL Server查询一项的树路径 [英] Sql Server query for tree path of one item

问题描述

我需要一个SQL查询，为我提供一项的完整树路径.这些表看起来像这样，并且MyItem_MyItemId和MyItemMapping_MyItemId之间存在1:n关系.

I need a SQL query giving me the complete tree path of one item. The tables Looks like this and there is a 1:n relation between MyItem_MyItemId and MyItemMapping_MyItemId.

表MyItem:

MyItem_MyItemId | MyItem_Title 
1 | Desktop
2 | Workspace
3 | Folder1
4 | Folder2
5 | Folder3
6 | Folder4
...

表MyItemMapping:

Table MyItemMapping:

MyItemMapping_MyItemId | MyItemMapping_MyItemParentId
4 | 3
3 | 2
2 | 1
1 | NULL
5 | 2
6 | 2
...

现在我需要一个查询，它为Folder2带来路径，例如"Desktop \ Workspace \ Folder1 \ Folder2".

Now I Need a query the brings the path for the Folder2 like "Desktop\Workspace\Folder1\Folder2.

我用递归查询(见下文)进行了尝试，但是SQL Server需要大约10秒钟才能解决它.我的数据库中只有5000条记录.我可以弄清楚，通过此查询，将为所有5000条记录计算路径，但是我只需要一项即可.有人可以帮我吗?

I tried it with a Recursive Query (see below) but SQL Server Needs about 10 seconds to resolve it. I have only 5000 records in database. I could figure out that with this query, the path is calculated for all 5000 records but I Need it only of one item. Can anybody help me?

WITH 
MyTable as
(
 select MyItem_MyItemId, MyItem_Title, MyItemMapping_MyItemParentId 
 from MyItem inner join MyItemMapping on MyItem_MyItemId = MyItemMapping_MyItemId
),
RecursiveTable AS 
(
  select t.MyItem_MyItemId, t.MyItem_Title, t.MyItemMapping_MyItemParentId
  from MyTable as t
  Where MyItemMapping_MyItemParentId is null 
  union all
  select  t.MyItem_MyItemId,  CAST(RecursiveTable.MyItem_Title + '\' + t.MyItem_Title AS NVARCHAR(max)), t.MyItemMapping_MyItemParentId
  from MyTable as t
  JOIN RecursiveTable ON RecursiveTable.MyItem_MyItemId = t.MyItemMapping_MyItemParentId
)   
select MyItem_Title from RecursiveTable where MyItem_MyItemid = 4

非常感谢.

最好的问候.马克

推荐答案

向相反方向移动.选择必要的项目后，将模式与 FOR XML 子句一起使用，以创建反斜杠分隔的有效值列表.

Move in the opposite direction. After selected is necessary items, use pattern with FOR XML clause for creating a list of backslash delimited valid values.

DECLARE @MyItemMapping_MyItemId int = 4
;WITH cte AS
 (
  SELECT MyItemMapping_MyItemId, MyItemMapping_MyItemParentId, 1 AS rn
  FROM MyItemMapping
  Where MyItemMapping_MyItemId = @MyItemMapping_MyItemId 
  UNION ALL
  SELECT m.MyItemMapping_MyItemId, m.MyItemMapping_MyItemParentId, rn + 1
  FROM MyItemMapping m JOIN cte c ON c.MyItemMapping_MyItemParentId = m.MyItemMapping_MyItemId
  )
  SELECT STUFF((SELECT '/' + m.MyItem_Title                   
                FROM cte c JOIN MyItem m                 
                  ON c.MyItemMapping_MyItemId = m.MyItem_MyItemId
                ORDER BY c.rn DESC                    
                FOR XML PATH, TYPE).value('.[1]', 'nvarchar(max)'), 1, 1, '') AS pathFolder 

pathFolder

pathFolder

结果:

PathFolder

Desktop/Workspace/Folder1/Folder2

在 SQLFiddle

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