The most efficient way to index and query paths in a graph

I have a table representing a graph: Edges (from, to) .

I would like to query this table using "path queries", getting only the source and destination of the path.

For example, suppose my table consists of the following rows:

+------+----+
| from | to |
+------+----+
| a    | b  |
| b    | c  |
| c    | d  |
| f    | g  |
| b    | f  |
| c    | a  |
+------+----+ 

Suppose I execute the following (pseudo) query:

SELECT ?v1, ?v2 WHERE ?v1 to ?t1, ?t1 to ?t2, ?t2 to ?v2;

This means that I want all source and destination pairs to exist in all 4-node paths. Executing this query should return the following results:

+-----+-----+
| ?v1 | ?v2 |
+-----+-----+
| a   | a   |
| a   | g   |
| a   | d   |
+-----+-----+

Of course, paths consisting of a different number of nodes may be needed, number 4 is not hard-coded :-)

My questions:

• SQL- ( , SQLite, ).
• . ? , ? ?

• (E.G "a - a" ).

• .

!