如何在下表中获得每个最小值和最大值对应的行号

SELECT t.id,
       MIN(CASE WHEN t.h = sub.h1 THEN n1 END) AS n1,
       MIN(CASE WHEN t.l = sub.l1 THEN n2 END) AS n2
FROM tab_name t
JOIN (SELECT id, MAX(h) AS h1, MIN(l) AS l1
      FROM tab_name
      GROUP BY id) sub
  ON t.id = sub.id
 AND (t.h = sub.h1 OR t.l = sub.l1)
GROUP BY t.id;

SELECT id, 
       min(h) as min_h,
       max(h) as max_h,
       max( case when low_rn = 1 then n1 end) as n1_for_min,
       min( case when high_rn = 1 then n1 end) as n1_for_max
FROM (
  SELECT *,
        row_number() over (partition by id order by h) as low_rn,
        row_number() over (partition by id order by h desc) as high_rn
  FROM mytable
) x 
WHERE 1 IN (low_rn, high_rn)
GROUP BY id

https://dbfiddle.uk/?rdbms=postgres_10&fiddle=35fcb41891a8a446bcb55f0a6fd0a774

first_value() select distinct

select distinct id,
       first_value(n1) over (partition by id order by h desc) as n1_at_max_h,
       first_value(n2) over (partition by id order by l desc) as n2_at_max_l
from t;

select id,
       ( array_agg(n1 order by h desc) )[1] as n1_at_max_h,
       ( array_agg(n2 order by l desc) )[1] as n2_at_max_l
from t
group by id;