从 SQL 中的邻接列表构建枚举路径

Question

初始场景

我的软件使用树数据结构，并将其存储在 SQL 中。 我使用名为Adjacency List的抽象，它由存储ID和ParentID的每一行组成。

ID是主键， ParentID是同一个表的外键。

问题

我想将我的 SQL 抽象“转换”为Path Enumeration 。 它由存储ID的每一行和存储ID路径的varchar字段组成，从根到当前行。 例如，这棵树中ID = 6行的Path字段：

将是/1/2/4/6/ 。 此处有更多详细信息，名称为Lineage Column 。

题

如何从只有ID和ParentID的现有数据库构建列Path ？

Answer 1

SQL Server 2005 及更高版本应支持以下内容：

WITH
  recursed_tree AS
(
  SELECT
    IDObject,
    concat('/', cast(IDObject as varchar(100)))   AS Path
  FROM
    tbObject
  WHERE
    ParentID IS NULL

  UNION ALL

  SELECT
    next.IDObject,
    concat(prev.Path, '/', cast(next.IDObject as varchar(100)))   AS Path
  FROM
    recursed_tree   AS prev
  INNER JOIN
    tbObject        AS next
       ON prev.IDObject = next.ParentID
)

SELECT
  *
FROM
  recursed_tree

Answer 2

我想出了这个 SQL Server 查询：

[ tbObjectHierarchy有一个名为IDObject的 FK 和 PK 以及一个名为Path的varchar ]

declare @T  as table (IDObject int, Path varchar(500))
declare @T2 as table (IDObject int, Path varchar(500))

insert into tbObjectHierarchy(IDObject, Path)
select o.IDObject, concat('/', cast(o.IDObject as varchar(100)), '/') as Path
from tbObject as o 
where o.ParentID is null

insert into @T (IDObject, Path)
select o.IDObject, concat(h.Path, cast(o.IDObject as varchar(100)), '/') as Path
from tbObject as o
inner join tbObjectHierarchy as h
on o.ParentID = h.IDObject

while exists (select top 1 * from @T)
begin
    insert into tbObjectHierarchy (IDObject, Path)
    select t.IDObject, t.Path
    from @T as t

    delete from @T2

    insert into @T2
    select o.IDObject, concat(t.Path, cast(o.IDObject as varchar(100)), '/') as Path
    from tbObject as o
    inner join @T as t
    on o.ParentID = t.IDObject

    delete from @T

    insert into @T
    select * from @T2
end