PostgreSQL-最短路徑

Question

我有一個網格表，其中存儲一個起點和一個目的地點。 看起來像這樣：

  src  | dest  | cost 
-------+-------+------
 {1,1} | {1,2} |    1
 {1,1} | {2,1} |    1
 {1,2} | {1,1} |    1
 {1,2} | {1,3} |    1
 {1,2} | {2,2} |    1
 ...
 {4,5} | {5,5} |    1

我想從我的起點開始，然后到它的鄰居之一，再到他的鄰居，依此類推。

到目前為止，我有這段代碼（計數器只是為了確保我不會陷入無限循環中）：

WITH RECURSIVE

init (here, there, cost_to_here, counter, path ) AS (
SELECT g.src, g.dest, 0.0, 1, array[g.src, g.dest]  -- SourcePoint with a cost of 0 src -> src
FROM grid AS g
WHERE g.src = '{1,1}'

UNION ALL

(WITH init(here, there, cost_to_here, counter, path) AS (TABLE init)  -- Reference the working Table once

SELECT g.src, g.dest, i1.cost_to_here + g.cost, i1.counter + 1, i1.path || array[g.dest]
FROM grid AS g, init AS i1
WHERE g.src = i1.there
AND NOT g.dest = ANY(i1.path)
AND (i1.here) IN (select i2.here
                   from init as i2)
and i1.counter < 7


 )
)
table init;

我從src點{1,1}並訪問它的鄰居。 由於我不想回到已經訪問過的地點，因此請檢查是否已經訪問了下一個地點。

這是代碼的作用：

 here  | there | cost_to_here | counter |                               path                                
-------+-------+--------------+---------+--------------------------------------
 {1,1} | {1,2} |          0.0 |       1 | {"{1,1}","{1,2}"}
 {1,1} | {2,1} |          0.0 |       1 | {"{1,1}","{2,1}"}
 {1,2} | {1,3} |          1.0 |       2 | {"{1,1}","{1,2}","{1,3}"}
 {1,2} | {2,2} |          1.0 |       2 | {"{1,1}","{1,2}","{2,2}"}
 {2,1} | {2,2} |          1.0 |       2 | {"{1,1}","{2,1}","{2,2}"}
 ...
 {1,2} | {1,3} |          3.0 |       4 | {"{1,1}","{2,1}","{2,2}","{1,2}","{1,3}"}
 {2,3} | {1,3} |          3.0 |       4 | {"{1,1}","{1,2}","{2,2}","{2,3}","{1,3}"}

如您所見，它為我生成了通往{1,3}不同路徑。 我如何才能保持最好的狀態？

但是我只想保持最好的道路。 我該如何處理？

Answer 1

然后，保持最短的一個。 像這樣：

select distinct on (src, dest) i.*
from init 8
order by src, dest, cost_to_here;