how to get the distance of sequence of nodes in pgr_dijkstra pgrouting?

Question

I have an array of integers(nodes or destinations) ie array[2,3,4,5,6,8] that need to be visited in the given sequence. What I want is, to get the shortest distance using pgr_dijkstra. But the pgr_dijkstra finds the shortest path for two points, therefore I need to find the distance of each pair using pgr_dijkstra and adding all distances to get the total distance. The pairs will be like
2,3
3,4

4,5

5,6

6,8. Is there any way to define a function that takes this array and finds the shortest path using pgr_dijkstra.

Query is: for 1st pair(2,3) SELECT * FROM pgr_dijkstra('SELECT gid as id,source, target, rcost_len AS cost FROM finalroads',2,3, false);

for 2nd pair(3,4) SELECT * FROM pgr_dijkstra('SELECT gid as id,source, target, rcost_len AS cost FROM finalroads'***,3,4,*** false)

for 3rd pair(4,5) SELECT * FROM pgr_dijkstra('SELECT gid as id,source, target, rcost_len AS cost FROM finalroads'***,4,5,*** false) ;

NOTE: The array size is not fixed, it can be different.

Is there any way to automate this in postgres sql may be using a loop etc? Please let me know how to do it. Thank you.

Answer 1

Using the solution provided in this post that makes use of a source table , it is possible to use your array. Note that the orig is your array omitting the last entry, and the dest omits the 1st entry.

SELECT 
  source, 
  target,
  (SELECT SUM(cost) FROM  -- or whatever you want to do with the routing result
     (SELECT * 
      FROM pgr_dijkstra('SELECT gid as id,source, target, rcost_len AS cost FROM finalroads',
                        orig,
                        dest, 
                        false))
     ) AS foo 
  ) AS cost
FROM (
  select unnest(myarray[:array_upper(myarray,1)-1])  as orig,
         unnest(myarray[2:]) as dest 
  from (select array[1,2,3,4] myarray) b) c;

Answer 2

If you want all pairs distance then use

select * from pgr_apspJohnson ('SELECT gid as id,source, target, rcost_len AS cost FROM finalroads)