EXPLAIN ANALYZE
SELECT *
FROM tparent JOIN tchild ON tchild.par_id = tparent.id
WHERE tparent.ord BETWEEN 1 AND 4
ORDER BY tparent.ord, tchild.ord;

                                                              QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------
 Sort  (cost=100000132.10..100000140.10 rows=8 width=16) (actual time=0.302..0.319 rows=9 loops=1)
   Sort Key: tparent.ord, tchild.ord
   ->  Nested Loop  (cost=0.00..84.10 rows=8 width=16) (actual time=0.181..0.267 rows=9 loops=1)
         ->  Index Scan using par_uniq_ord on tparent  (cost=0.00..20.40 rows=4 width=8) (actual time=0.100..0.109 rows=4 loops=1)
               Index Cond: ((ord >= 1) AND (ord <= 4))
         ->  Index Scan using chi_pkey_parid_ord on tchild  (cost=0.00..9.93 rows=2 width=8) (actual time=0.020..0.026 rows=2 loops=4)
               Index Cond: (tchild.par_id = "outer".id)
 Total runtime: 0.412 ms
(8 rows)