adds initial version of distance matrix function

src/pg/sql/26_distance_matrix.sql

@@ -0,0 +1,45 @@
+-- Calculate the distance matrix using underlying road network
+-- Sample usage:
+--   select * from cdb_distancematrix("fake_drains", "cvxopt_fake_sources")
+CREATE OR REPLACE FUNCTION CDB_DistanceMatrix(
+    origin_table regclass,
+    destination_table regclass,
+    transit_mode text DEFAULT 'car')
+    RETURNS TABLE(origin_id bigint, destination_id bigint,
+                  the_geom geometry(geometry, 4326),
+                  length_km numeric, duration_sec numeric)
+AS $$
+DECLARE
+    query_string text;
+BEGIN
+    query_string := format('
+        WITH pairs AS (
+            SELECT
+                o."cartodb_id" AS origin_id,
+                d."cartodb_id" AS destination_id,
+                o."the_geom" AS origin_point,
+                d."the_geom" AS destination_point
+            FROM
+                (SELECT * FROM %I) AS o,
+                (SELECT * FROM %I) AS d),
+        results AS (
+            SELECT
+                origin_id,
+                destination_id,
+                (cdb_route_point_to_point(origin_point,
+                                          destination_point,
+                                          ''%s'')).*
+            FROM pairs)
+        SELECT
+            origin_id::bigint AS origin_id,
+            destination_id::bigint AS destination_id,
+            shape AS the_geom,
+            length::numeric AS length_km,
+            duration::numeric AS duration_sec
+        FROM results;', origin_table, destination_table, transit_mode);
+    RAISE NOTICE '%', query_string;
+    RETURN QUERY
+    EXECUTE query_string;
+    RETURN;
+END;
+$$ LANGUAGE plpgsql;