如何遍历 table 中带有 id 和 parentId 的路径？

Question

假设我有一个 table 比如：

id    |   parentId   |  name
 1          NULL         A
 2            1          B
 3            2          C
 4            1          E
 5            3          E

我正在尝试编写一个我可以调用的标量函数：

SELECT dbo.GetId('A/B/C/E') 如果我们使用上面的引用 table，将产生“5”。该函数将执行以下步骤：

Find the ID of 'A' which is 1

Find the ID of 'B' whose parent is 'A' (id:1) which would be id:2

Find the ID of 'C' whose parent is 'B' (id:2) which would be id:3

Find the ID of 'E' whose parent is 'C' (id:3) which would be id:5

我试图用一个 WHILE 循环来完成它，但是它变得非常复杂非常快......只是认为必须有一个简单的方法来做到这一点。

Answer 1

我想我是根据@SeanLange 的建议使用递归 CTE（在评论中）：

CREATE FUNCTION GetID 
(
    @path VARCHAR(MAX)
)

/* TEST:
SELECT dbo.GetID('A/B/C/E')

*/
RETURNS INT 
AS
BEGIN
    DECLARE @ID INT;

    WITH cte AS (
        SELECT p.id ,
               p.parentId ,
               CAST(p.name AS VARCHAR(MAX)) AS name
        FROM tblT p
        WHERE parentId IS NULL

        UNION ALL
        SELECT p.id ,
               p.parentId ,
               CAST(pcte.name + '/' + p.name AS VARCHAR(MAX)) AS name
        FROM dbo.tblT p
        INNER JOIN cte pcte ON
            pcte.id = p.parentId
    )
    SELECT @ID = id
    FROM cte
    WHERE name = @path

    RETURN @ID
END

Answer 2

这是一个基于您的示例数据和我理解的要求的功能性 rcte 示例。

if OBJECT_ID('tempdb..#Something') is not null
    drop table #Something

create table #Something
(
    id int
    , parentId int
    , name char(1)
)

insert #Something
select 1, NULL, 'A' union all
select 2, 1, 'B' union all
select 3, 2, 'C' union all
select 4, 1, 'E' union all
select 5, 3, 'E'

declare @Root char(1) = 'A';

with MyData as
(
    select *
    from #Something
    where name = @Root

    union all

    select s.*
    from #Something s
    join MyData d on d.id = s.parentId
)

select *
from MyData

请注意，如果您更改变量的值，输出将会调整。我会将其设为内联 table 值函数。

Answer 3

CTE 版本未优化获取分层数据的方式。 (Refer MSDN Blog)

你应该像下面提到的那样做。它经过了 1000 万条记录的测试，比 CTE 版本快 300 倍:)

Declare @table table(Id int, ParentId int, Name varchar(10))
insert into @table values(1,NULL,'A')
insert into @table values(2,1,'B')
insert into @table values(3,2,'C')
insert into @table values(4,1,'E')
insert into @table values(5,3,'E')

DECLARE @Counter tinyint = 0;

IF OBJECT_ID('TEMPDB..#ITEM') IS NOT NULL
DROP TABLE #ITEM

CREATE TABLE #ITEM
(
 ID int not null 
,ParentID int
,Name VARCHAR(MAX)
,lvl int not null
,RootID int not null
)

INSERT INTO #ITEM
    (ID,lvl,ParentID,Name,RootID)
SELECT   Id
        ,0 AS LVL
        ,ParentId
        ,Name
        ,Id AS RootID
FROM            
    @table
WHERE
        ISNULL(ParentId,-1) = -1

WHILE @@ROWCOUNT > 0
    BEGIN
        SET @Counter += 1
        insert into #ITEM(ID,ParentId,Name,lvl,RootID)
        SELECT  ci.ID
                ,ci.ParentId
                ,ci.Name
                ,@Counter as cntr
                ,ch.RootID
        FROM    
            @table AS ci
        INNER JOIN
            #ITEM AS pr 
        ON
            CI.ParentId=PR.ID
        LEFT OUTER JOIN
            #ITEM AS ch
        ON  ch.ID=pr.ID
        WHERE           
                ISNULL(ci.ParentId, -1) > 0
            AND PR.lvl = @Counter - 1
END

select * from #ITEM

如何遍历 table 中带有 id 和 parentId 的路径？

How to traverse a path in a table with id & parentId?

sql

sql-server

recursive-query

hierarchical-data