将这个层面桌子反正规化成平台的最快/最简单方法是什么？

Question

我有以下分层表：

Table Category:
CategoryId, ParentCategoryId, CategoryName
1, null, SomeRoot
2, 1, SomeChild
3, 2, SomeGrandchild
4, 3, SomeGreatGrandchild

（请注意，此示例数据不包含比级别4更早的节点上的叶子，但这是可能的）。如果相关，数据将永远不会超过第4级。我想将它转换/转换到这个固定的4级显示器

CatId, Name1, Name2, Name3, Name4
1, SomeRoot, null, null, null
2, SomeRoot, SomeChild, null, null
3, SomeRoot, SomeChild, SomeGrandchild, null
4, SomeRoot, SomeChild, SomeGrandchild, SomeGreatGrandchild

我已经做了4次左外连接到类别表，并构建了一个巨大的case语句来检测用于ID字段的级别，但是不包括空行....任何想法？救命！

Answer 1

这可能不是最有效的查询，但它是最容易编码的：

declare @YourTable table (CategoryId int primary key, ParentCategoryId int , CategoryName varchar(50))

INSERT INTO @YourTable VALUES (1, null, 'SomeRoot')
INSERT INTO @YourTable VALUES (2, 1, 'SomeChild')
INSERT INTO @YourTable VALUES (3, 2, 'SomeGrandchild')
INSERT INTO @YourTable VALUES (4, 3, 'SomeGreatGrandchild')

INSERT INTO @YourTable VALUES (10, null, 'X_SomeRoot')
INSERT INTO @YourTable VALUES (20, 10, 'X_SomeChild')
INSERT INTO @YourTable VALUES (30, 20, 'X_SomeGrandchild')


Select
    c1.CategoryId, c1.CategoryName, c2.CategoryName, c3.CategoryName, c4.CategoryName
    From @YourTable          c1
        INNER JOIN @YourTable c2 On c1.CategoryId = c2.ParentCategoryId
        INNER JOIN @YourTable c3 On c2.CategoryId = c3.ParentCategoryId
        INNER JOIN @YourTable c4 On c3.CategoryId = c4.ParentCategoryId
    WHERE c1.ParentCategoryId IS NULL 
UNION
Select
    c1.CategoryId, c1.CategoryName, c2.CategoryName, c3.CategoryName, NULL
    From @YourTable          c1
        INNER JOIN @YourTable c2 On c1.CategoryId = c2.ParentCategoryId
        INNER JOIN @YourTable c3 On c2.CategoryId = c3.ParentCategoryId
    WHERE c1.ParentCategoryId IS NULL
UNION
Select
    c1.CategoryId, c1.CategoryName, c2.CategoryName, NULL, NULL
    From @YourTable          c1
        INNER JOIN @YourTable c2 On c1.CategoryId = c2.ParentCategoryId
    WHERE c1.ParentCategoryId IS NULL
UNION
Select
    c1.CategoryId, c1.CategoryName, NULL, NULL, NULL
    From @YourTable          c1
    WHERE c1.ParentCategoryId IS NULL
ORDER BY 2,3,4,5

OUTPUT：

SortB CategoryId  CategoryName CategoryName  CategoryName      CategoryName
----- ----------- ------------ ------------- ----------------- --------------------
1     1           SomeRoot     NULL          NULL              NULL
2     1           SomeRoot     SomeChild     NULL              NULL
3     1           SomeRoot     SomeChild     SomeGrandchild    NULL
4     1           SomeRoot     SomeChild     SomeGrandchild    SomeGreatGrandchild
1     10          X_SomeRoot   NULL          NULL              NULL
2     10          X_SomeRoot   X_SomeChild   NULL              NULL
3     10          X_SomeRoot   X_SomeChild   X_SomeGrandchild  NULL

(7 row(s) affected)

Answer 2

试试这个：

  Select C.CatId, C.Name, PC.Name, GP.Name, GGP.Name
  From Category C
    Left Join Category PC On PC.CatId = C.ParentCategoryId
    Left Join Category GP On GP .CatId = PC.ParentCategoryId
    Left Join Category GGP On GGP .CatId = GP.ParentCategoryId

根据您的评论，如果您编写UDF如下：

Create Function CatParentNames
( @CatId Integer )
Returns varchar(1000)
AS
Begin
     Declare @outVal VarChar(1000)
     Declare @ParId Integer
     Select @ParId = ParentCategoryId, @outVal = Name
     From Category 
     Where CatId = @CatId
     While Exists(Select * From Category 
                  Where CatId = @ParId)
        Begin
           Select @ParId = ParentCategoryId, 
                 @outVal = Name + ', ' + @outVal
           From Category 
           Where CatId = @ParId
        End

 Return @outVal

End

然后，编写你的sql如下：

Select CatId, dbo.CatParentNames(CatId)
From Category
Where ParentCategoryId Is Not Null

Answer 3

试试这个：

select a.CategoryId as CatId, 
a.CategoryName as Name1, 
cast(null as varchar(20)) as Name2, 
cast(null as varchar(20)) as Name3,
cast(null as varchar(20)) as Name4
from @YourTable a
where a.ParentCategoryId is null

union all

select b.CategoryId, 
a.CategoryName, 
b.CategoryName,
null,
null
from @YourTable a
inner join @YourTable b
on a.CategoryId = b.ParentCategoryId
where a.ParentCategoryId is null


union all

select c.CategoryId, 
a.CategoryName, 
b.CategoryName, 
c.CategoryName, 
null
from @YourTable a
inner join @YourTable b
on a.CategoryId = b.ParentCategoryId
inner join @YourTable c
on b.CategoryId = c.ParentCategoryId
where a.ParentCategoryId is null

union all 

select d.CategoryId, 
a.CategoryName, 
b.CategoryName, 
c.CategoryName, 
d.CategoryName
from @YourTable a
inner join @YourTable b
on a.CategoryId = b.ParentCategoryId
inner join @YourTable c
on b.CategoryId = c.ParentCategoryId
inner join @YourTable d
on c.CategoryId = d.ParentCategoryId
order by 2, 3, 4, 5

但是，如果要将其用于如下所示的多列TreeView，那么这不是构建它的方法：

（来源：digitaltools.com）

更多可以找到here.