Grouped LIMIT in PostgreSQL: show the first N rows for each group?
Since v9.3 you can do a lateral join
select distinct t_outer.section_id, t_top.id, t_top.name from t t_outer
join lateral (
select * from t t_inner
where t_inner.section_id = t_outer.section_id
order by t_inner.name
limit 2
) t_top on true
order by t_outer.section_id;
It might be faster but, of course, you should test performance specifically on your data and use case.
Here's another solution (PostgreSQL <= 8.3).
SELECT
*
FROM
xxx a
WHERE (
SELECT
COUNT(*)
FROM
xxx
WHERE
section_id = a.section_id
AND
name <= a.name
) <= 2
New solution (PostgreSQL 8.4)
SELECT
*
FROM (
SELECT
ROW_NUMBER() OVER (PARTITION BY section_id ORDER BY name) AS r,
t.*
FROM
xxx t) x
WHERE
x.r <= 2;