psql=# table b;
 l │ r
───┼───
 a │ b
 b │ e
 e │ d
(3 rows)

Time: 0.188 ms
psql=# with recursive c as (select * from b union select b.l, c.r from b join c on c.l = b.r) table c;
 l │ r
───┼───
 a │ b
 b │ e
 e │ d
 a │ e
 b │ d
 a │ d
(6 rows)