如何从 SQL 表中检索分层数据? [英] How to retrieve hierarchical data from a SQL Table?

问题描述

我有下面的存储过程来返回 Id、parentId 和 absoluteUrls 的列表，它们工作正常:

I have got the below stored procedure to return the list of Id, parentId and absoluteUrls which works fine:

ALTER PROCEDURE [dbo].[SearchDataManager.HierarchyById] 
    @currentId AS int   
AS
BEGIN
 DECLARE @id INT 
 DECLARE @parentId INT
 DECLARE @absoluteUrl NVARCHAR(1000)

 DECLARE @Hierarchy TABLE (Id int, ParentId int, AbsoluteUrl nvarchar(1000))

 WHILE @currentId != 0
 BEGIN

     SELECT @id = Id, @parentId = ParentId, @absoluteUrl = AbsoluteUrl
     FROM dbo.[SearchDataManager.NiceUrls]
     WHERE id = @currentId

     INSERT INTO @Hierarchy  VALUES (@id, @parentId, @absoluteUrl)

    SET @currentId = @parentId
 END

    SELECT * FROM @Hierarchy  
END

NiceUrls"表具有 Id 和 ParentId.parentId 指的是同一张表中的一条记录.

The "NiceUrls" table has Id and ParentId. parentId refers to a record in the same table.

它返回如下:

 ----------------------------------
    Id  | ParentId | AbsoluteUrl
    ----------------------------------
    294 | 5        | url1
    5   | 2        | url2
    2   | 0        | url3

上面的代码使用 WHILE 循环并定义一个 Table 变量可以正常工作，但我只是想知道有没有更好的方法从表中检索层次结构数据?

The above code works fine using a WHILE loop and defining a Table variable but I'm just wondering is there any better way to retrieve hierarchy data from a table?

上面代码的问题是可维护性.如果我需要再返回 NiceUrls 表的 1 列，那么我必须定义一个新变量，将该列添加到内联表中，等等.

The problem with the above code is maintainability. If I'd need to return 1 more column of the NiceUrls table then I'd have to define a new variable, add the column to the inline table, etc.

有没有更好的方法重写sp?

Is there any better way to rewrite the sp?

谢谢，

是什么

推荐答案

with Hierarchy (Id, ParentId, AbsoluteUrl, Level)
 AS
 (
    -- anchor member
     SELECT Id,
        ParentId,
        AbsoluteUrl,
        0 AS Level   
     FROM dbo.[NiceUrls]
     WHERE id = @currentId
     UNION ALL
     -- recursive members
     SELECT su.Id,
        su.ParentId,
        su.AbsoluteUrl,
        Level + 1 AS Level   
     FROM dbo.[NiceUrls] AS su
     INNER JOIN Hierarchy ON Hierarchy.ParentId = su.Id  
 )
 SELECT * FROM Hierarchy

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