以下情況下的SQL查詢

Question

我有一個包含數千條記錄的processDependency表。樣本記錄給出如下：

Proc DepProc 
P1 P2 
P2 P3 
P3 P4 
P4 P5 
P6 P7 

所以，當我運行SQL查詢我應該能夠如下推導：

1. P1-P2-P3-P4-P5

2. P6，P7

   任何人都可以幫助我與一般的SQL。

Answer 1

這是不完全正確，因爲它會從PROC

所有路徑，但你並沒有明確哪一個應該首先使用。

無論如何它應該給你一個想法。

SELECT recurse AS 
(
    SELECT Proc AS Start, 
      Proc||COALESCE('-'||DepProc,'') AS PATH, 
      DepProc as Next, 1 as Level 
    FROM table 

    UNION ALL 

    SELECT Start, 
      PATH||'-'||t.DepProc, 
      t.DepProc as Next, 
      Level+1 as Level 
    FROM recurse r 
    JOIN table t ON r.Next = t.Proc 
), recurseWithMax AS 
(
    SELECT PATH, Start, MAX(Level) OVER (Partition by Start) as Max, Level 
) 
SELECT Start, PATH 
FROM recurseWithMax 
WHERE Level = Max