Question

我正在尝试压缩/组合表中的行与父子层次结构。我试图找出每个链接的开头和结尾。 - 如果 a 与 b 相关联，则 b 与 c 相关联，然后 c < / strong>与 d 相关联，我希望输出将 a 链接到 d 。

我尽量避免使用带循环的程序，所以任何建议都会非常感激！

原始数据集和所需输出如下：

personID | form | linkedform ---------|---------|--------- 1 | a | b 1 | b | c 1 | c | d 1 | d | NULL 2 | e | f 2 | f | g 2 | g | NULL 2 | h | i 2 | i | NULL 3 | j | NULL 3 | k | l 3 | l | NULL

期望的输出：

personID | form | linkedform ---------|---------|--------- 1 | a | d 2 | e | g 2 | h | i 3 | j | NULL 3 | k | l

每个personID可以有多个链接，链接只能由一个或多个表单组成。

Answer 1

-- use a recursive cte to build the hierarchy
-- start with [linkedform] = null and work your way up
;WITH cte AS 
(
    SELECT  *, [form] AS [root],
            1 AS [Level]
    FROM    Table1
    WHERE   [linkedform] IS NULL
    UNION ALL  
    SELECT  t1.*,
            [root],
            [Level] + 1
    FROM    Table1 t1
    JOIN    cte ON cte.form = t1.linkedform
)
-- level 1 will be the last element, use row_number to get the first element
-- join the two together based on last and first level, that have the same personid and root ([linkedform] = null)
SELECT  cte.personId,
        cte2.form, 
        cte.form
FROM    cte
        JOIN (  SELECT  *, 
                        ROW_NUMBER() OVER (PARTITION BY personId, [root] ORDER BY Level DESC) Rn 
                FROM    cte) cte2 
            ON cte2.Rn = cte.Level 
                AND cte2.personId = cte.personId
                AND cte2.root = cte.root
WHERE   cte.[Level] = 1
ORDER BY cte.personId, cte2.form

结合父子行 - TSQL

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