这是一个针对在特定分类（id=19）中回复帖子的用户的徽章查询。post_number > 1 确保这是回复，而不是首帖。
SELECT DISTINCT ON (p.user_id)
p.user_id, p.id AS post_id, p.created_at AS granted_at
FROM badge_posts p
JOIN topics t ON t.id = p.topic_id
WHERE category_id = 19 AND p.post_number > 1
AND (:backfill OR p.id IN (:post_ids))