>> The table at hand is more a kind of a collection of graphs where I
want to find all possible paths between a given starting point and a
given end point. <<
For the reachabiity index of a general graph, you need Warshal's
algorithm.
Let V = number of nodes in the graph
Let A[i,j] be the adjacency matrix for the undirected graph
FOR j:= 1 TO VDO FOR i:= 1 TO V DO IF A[i,j] = 1 THEN FOR k := 1 TO V DO IF A[j,k]] = 1
THEN A[i,k]] := 1;
You can also do a summation to get the length of the path from i to j.
You can concatenate names of the nodes into a string that gives the
path, etc.
Her is a first attempt at some SQL; I am sure it can be done better
CREATE TABLE Graph
(i CHAR(2) NOT NULL,j CHAR(2) NOT NULL,flag CHAR(1) NOT NULL DEFAULT 'n' CHECK (flag IN ('n', 'y')),PRIMARY KEY
(i,j));
INSERT INTO Graph (i, j, flag)SELECT DISTINCT G1.i, G2.j, 'y' FROM Graph AS G1, Graph AS G1 WHERE G1.i <> G2.j AND
EXISTS (SELECT * FROM Graph AS G3 WHERE G3.i = G1.j AND G3.j = G2.i) AND NOT EXISTS
(SELECT * FROM Graph AS G3 WHERE (G3.i = G1.i AND G3.j = G1.j)) OR (G3.i = G2.i AND G3.j
=G2.j));
You wll have to run this statement until the size of Graph does not
change -- no new rows are being added.