什么是好的Perl模式匹配/正则表达式模块？(What are good Perl Pattern-matching / Regex Modules?)

 由于您试图将树放入表的一部分，看起来您无论如何都需要使用SET IDENTITY_INSERT ON 。 您需要确保新树有空间。 在这种情况下，我假设49是表中当前的最大id ，因此我们不需要担心超出表中后面的树。 
 
 您需要能够将ID从旧树映射到新树。 除非有一些围绕id的规则，只要它准确，确切的映射应该是无关紧要的，所以在这种情况下，我只是做这样的事情： 
 
SET IDENTITY_INSERT dbo.Relations ON

;WITH CTE_MappedIDs AS
(
    SELECT
        old_id,
        ROW_NUMBER() OVER(ORDER BY old_id) + 49 AS new_id
    FROM
    (
        SELECT DISTINCT parent AS old_id FROM #relationtree
        UNION
        SELECT DISTINCT child AS old_id FROM #relationtree
    ) SQ
)
INSERT INTO dbo.Relations (Id, ParentId)
SELECT
    CID.new_id,
    PID.new_id
FROM
    #relationtree RT
INNER JOIN CTE_MappedIDs PID ON PID.old_id = RT.parent
INNER JOIN CTE_MappedIDs CID ON CID.old_id = RT.parent
-- We need to also add the root node
UNION ALL
SELECT
    NID.new_id,
    NULL
FROM
    #relationtree RT2
INNER JOIN CTE_MappedIDs NID ON NID.old_id = RT2.parent
WHERE
    RT2.parent NOT IN (SELECT DISTINCT child FROM #relationtree)

SET IDENTITY_INSERT dbo.Relations OFF
 
 我没有测试过，但如果它没有按预期工作，那么希望它能指出你正确的方向。 

Since you're trying to put the tree into a segment of the table it looks like you're going to need to use SET IDENTITY_INSERT ON for the table anyway. You're going to need to make sure that there is room for the new tree. In this case, I'll assume that 49 is the current maximum id in your table so that we don't need to be concerned with overrunning a tree that's later in the table.
 
You'll need to be able to map the IDs from the old tree to the new tree. Unless there's some rule around the ids, the exact mapping should be irrelevant as long as it's accurate, so in that case, I'd just do something like this:
 
SET IDENTITY_INSERT dbo.Relations ON

;WITH CTE_MappedIDs AS
(
    SELECT
        old_id,
        ROW_NUMBER() OVER(ORDER BY old_id) + 49 AS new_id
    FROM
    (
        SELECT DISTINCT parent AS old_id FROM #relationtree
        UNION
        SELECT DISTINCT child AS old_id FROM #relationtree
    ) SQ
)
INSERT INTO dbo.Relations (Id, ParentId)
SELECT
    CID.new_id,
    PID.new_id
FROM
    #relationtree RT
INNER JOIN CTE_MappedIDs PID ON PID.old_id = RT.parent
INNER JOIN CTE_MappedIDs CID ON CID.old_id = RT.parent
-- We need to also add the root node
UNION ALL
SELECT
    NID.new_id,
    NULL
FROM
    #relationtree RT2
INNER JOIN CTE_MappedIDs NID ON NID.old_id = RT2.parent
WHERE
    RT2.parent NOT IN (SELECT DISTINCT child FROM #relationtree)

SET IDENTITY_INSERT dbo.Relations OFF
 
I haven't tested that, but if it doesn't work as expected then hopefully it will point you in the right direction.