create temp table graph0( f int, t int, label text );

insert into graph0 values
	(1, 2, 'arc 1 -> 2'),
	(1, 3, 'arc 1 -> 3'),
	(2, 3, 'arc 2 -> 3'),
	(1, 4, 'arc 1 -> 4'),
	(4, 5, 'arc 4 -> 5');

with recursive search_graph(f, t, label) as (
	select * from graph0 g
	union distinct
	select g.*
	from graph0 g, search_graph sg
	where g.f = sg.t
) search depth first by f, t set seq
select * from search_graph order by seq;