SQL Server：最长路径

Question

在SQL Server中，我在表格中的From和To列中有（From，To）。

From  To
-  -
1  5
1  7
1  8
1  17
2  11
3  5
4  7
5  12
5  13
5  17
8  13
8  17
13 17

如何找到作为输入给出的任意两个n点之间的最长路径？例如，如果输入为1,17，则答案应为1 - 5 - 13 - 17

Answer 1

<强> SQL DEMO

WITH Path ( FromID, ToID, Length, nodes ) AS (
     SELECT  t1.FromID, t1.ToID, 0 as Length, 
             CAST( t1.FromID AS VARCHAR(max) ) +'-'+ 
             CAST( t1.ToID AS VARCHAR(max) ) as nodes
     FROM Table1 t1
     UNION ALL
     SELECT P.FromID, t2.ToID, P.Length + 1, 
            P.nodes + '-' + CAST(t2.ToID AS VARCHAR(max) ) as nodes
     FROM Table1 t2
     JOIN Path  P
       ON P.ToID = t2.FromID
) 
SELECT *
FROM Path
WHERE FromID = 1
   and ToID = 17
Order by Length

<强>输出

从1到17，有两条长度为2的路径

| FromID | ToID | Length |     nodes |
|--------|------|--------|-----------|
|      1 |   17 |      0 |      1-17 |
|      1 |   17 |      1 |    1-8-17 |
|      1 |   17 |      1 |    1-5-17 |
|      1 |   17 |      2 | 1-5-13-17 |
|      1 |   17 |      2 | 1-8-13-17 |