sql-server-2005 – SQL查询：分层合并

Create Table [example] (
    id          Integer   Not Null Primary Key,parentID    Integer       Null,largeData1  nVarChar(max) Null,largeData2  nVarChar(max) Null);
    -- largeData3...n also exist

Insert Into [example] (id,parentID,largeData1,largeData2)
Select 1,null,'blah blah blah',null          Union
Select 2,1,null          Union
Select 3,'foo bar foobar',null          Union
Select 4,3,'lorem ipsum' Union
Select 5,4,null;

此数据的层次结构图：

我想编写一个查询,它将返回任何给定[id]值的单行.该行应包含该行的[id]和[parentID]信息.它还应包含[largeData1 … n]字段.但是,如果largeData字段为null,则它应该遍历层次结构,直到遇到该字段的非null值.简而言之,它应该像coalesce函数一样工作,除了行的层次结构而不是一组列.

例：

其中[id] = 1：

id:          1
parentID:    null
largeData1:  blah blah blah
largeData2:  null

其中[id] = 2

id:          1
parentID:    1
largeData1:  blah blah blah
largeData2:  null

其中[id] = 3

id:          3
parentID:    1
largeData1:  foo bar foobar
largeData2:  null

其中[id] = 4

id:          4
parentID:    3
largeData1:  foo bar foobar
largeData2:  lorem ipsum

其中[id] = 5

id:          5
parentID:    4
largeData1:  foo bar foobar
largeData2:  lorem ipsum

到目前为止,我有这个：

Declare @id Integer; Set @id = 5;

With heirarchy
    (id,largeData2,[level])
As (
    Select id,1 As [level]
    From example
    Where id = @id

    Union All

    Select parent.id,parent.parentID,parent.largeData1,parent.largeData2,child.[level] + 1 As [level]
    From example As parent
    Inner Join heirarchy As child
        On parent.id = child.parentID)

Select id,(Select top 1 largeData1
    From heirarchy
    Where largeData1 Is Not Null
    Order By [level] Asc) As largeData1,(Select top 1 largeData2
    From heirarchy
    Where largeData2 Is Not Null
    Order By [level] Asc) As largeData2

From example
Where [id] = @id;

这将返回我要查找的结果.但是,根据查询计划,它会为我撤回的每个largeData字段单独传递层次结构.

我怎样才能提高效率呢？

这显然是更复杂问题的简化版本.最终查询将以XML格式返回数据,因此涉及FOR XML子句的任何解决方案都非常好.

我可以为此创建一个CLR聚合函数,如果这样做会有所帮助.我还没有探索过这条路线.

解决方法

DECLARE @Id  int

SET @Id = 5


;WITH cte (Id,ParentId,SaveParentId,LargeData1,LargeData2)
 as (--  The "anchor",your target Id
     select
        ex.Id,ex.ParentId,ex.ParentId  SaveParentId  --  Not changed throughout the CTE,ex.LargeData1,ex.LargeData2
      from Example ex
      where ex.Id = @Id
     union all select
                 cte.Id,cte.SaveParentId  --  Not changed throughout the CTE
                 --  These next are only "reset" if they are null and a not-null
                 --  value was found at this level,isnull(ex.LargeData1,cte.LargeData2),isnull(ex.LargeData2,cte.LargeData2)
      from Example ex
       inner join cte
        on cte.ParentId = ex.Id)
 select
   Id,SaveParentId     ParentId,max(LargeData1)  LargeData1,max(LargeData2)  LargeData2
 from cte
 group by Id,SaveParentId

基本上,从目标节点开始并向上走树,在找到它们时将空列替换为非空值.

(抱歉,我周末不做XML.)

（编辑：李大同）

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