Question

我有很多产品已被淘汰并被其他产品取代。该表有2列：OriginalItem，SubstituteItem。

我想创建一个列表来保留OriginalItem，但用最近的替换替换SubtituteItem。因此，如果SubstitueItem位于OriginalItem列中，它将被替换。这可能发生1次或20次，这是我遇到困难的部分。

示例 - 原始列表

car1, car2    
car2, car3    
car3, car4

预期结果

car1, car4    
car2, car4    
car3, car4

感谢您的帮助!!

Answer 1

您可以使用recursive CTE执行此操作。像下面这样的东西可以让你进入球场：

WITH recCTE AS
(
    --recursive seed (Starting point) which will be every record in this case
    SELECT
        originalitem,
        substituteitem,
        1 as depth --track how many iterations
        CAST(originalitem + '>' + substituteitem AS NVARCHAR(500)) as path --track the full path from original item to substitute for fun
    FROM yourtable

    UNION ALL

    --recursive term (gets called over and over again until the join fails)
    SELECT
        recCTE.originalItem,
        yourtable.substituteitem,
        recCTE.depth + 1, --increment depth
        recCTE.path + ">" + yourtable.substituteitem --add to the path
    FROM
        recCTE  --this CTE provides the foundation for this statement because it's recursive
        INNER JOIN youttable ON
            recCTE.substituteitem = yourtable.originalitem --joining sub to orig
    WHERE depth < 20 --just in case of cycling
)
SELECT * FROM reccCTE;

2列列表 - 递归值替换 - SQL Server 2016

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