与其说是一个可用的答案，不如说是一个概念证明，这里有一个基于cte的版本。它使用 STRING_AGG 按顺序连接每个节点的子节点，然后用其子节点递归地替换每个节点以构建输出字符串—这意味着在节点键是彼此的子字符串的情况下，它将不起作用。

DECLARE @t TABLE 
(id CHAR(1) NOT NULL PRIMARY KEY,
 parentid CHAR(1) NULL,
 roworder TINYINT NOT NULL
)

INSERT @t (id, parentid, roworder)
VALUES('A', NULL, 0),
('B','A',0),
('C','A',1),
('D','C',0),
('E','C',1),
('F','C',2),
('G','E',0),-- two extra nodes to prove that this isn't a one-off
('H','E',1)

;WITH aggCTE
AS
(
    SELECT parentid, STRING_AGG(CONVERT(VARCHAR(MAX), id), ' ') WITHIN GROUP (ORDER BY Roworder) AS children
    FROM @t
    GROUP BY parentid

)
,recCTE
AS
(
    SELECT  a.parentid, 
            a.children,
            CAST(ISNULL(a.parentid,'') AS VARCHAR(MAX)) AS processed, --to prevent loops
            0 AS seq, --to pick the right output row
            a.children AS firstnode --to disambiguate if the data contains multiple trees
    FROM aggCTE AS a
    WHERE a.parentid IS NULL

    UNION ALL

    SELECT  a.parentid, 
            REPLACE(a.children, b.parentid, CONCAT(b.children, ' ', b.parentid)) AS children, 
            CONCAT(a.processed, b.parentid) AS processed, 
            a.seq + 1 AS seq, 
            a.firstnode
    FROM recCTE AS a
    JOIN aggCTE AS b
    ON CHARINDEX(b.parentid, a.children) > 0
    AND CHARINDEX(b.parentid, a.processed) = 0
)
,rnCTE
AS
(
    SELECT children,
            ROW_NUMBER() OVER (PARTITION BY firstnode ORDER BY seq DESC) AS rn
    FROM recCTE
)
SELECT children AS post_order_traversal
FROM rnCTE
WHERE rn = 1

只需按原样实施即可找到解决方案：

If(OBJECT_ID('tempdb..#result') Is Not Null) Drop Table #result;
If(OBJECT_ID('tempdb..#stack') Is Not Null) Drop Table #stack;

create table #result (id int not null identity primary key, [value] bigint null);
create table #stack (id int not null identity primary key, [value] bigint null);

INSERT INTO #stack values(null) --inserting root identifiers here

WHILE EXISTS (SELECT * FROM #stack)
BEGIN
    declare @stack_id int, @stack_value bigint
    select top 1 @stack_id=id, @stack_value=value from #stack order by id desc
    delete from #stack where id=@stack_id

        INSERT INTO #stack
        -- here comes our query, which should fetch children of specified id and order it
        select tos.id 
        from inputTable as t
        where (ISNULL(@stack_value, 0) = 0 AND t.ParentId IS NULL) OR (ISNULL(@stack_value, 0) != 0 AND t.ParentId = @stack_value)
        order by t.[order] asc

    insert into #result values(@stack_value)
END

select [value] from #result order by id desc

If(OBJECT_ID('tempdb..#result') Is Not Null) Drop Table #result;
If(OBJECT_ID('tempdb..#stack') Is Not Null) Drop Table #stack;

到目前为止，使用cte似乎是不可能的。