Convert a Linestring into a set of two-point segments

segments.sql

    CREATE TABLE lines ( 
      gid integer primary key, 
      geom geometry(Linestring, 4326)
    );

    INSERT INTO lines VALUES (1, 'SRID=4326;LINESTRING(1 1, 2 2, 3 3, 4 4)');
    INSERT INTO lines VALUES (2, 'SRID=4326;LINESTRING(0 1, 0 2, 0 3, 0 4)');

    SELECT ST_AsText((ST_Dump(ST_Split(lines.geom, points.geom))).geom)
    FROM
    (
      SELECT ST_Union(pt) geom FROM (
         SELECT gid, geom, (ST_DumpPoints(geom)).geom AS pt FROM lines) a
    ) points,
    lines