Answering my own question, here is a Data Explorer query to pull those users who have most recently done their first post:
-- date :start_date
SELECT u.id AS user_id, p.id AS post_id, p.created_at
FROM users u
JOIN user_stats us
ON u.id = us.user_id
JOIN posts p
ON u.id = p.user_id
WHERE p.created_at = us.first_post_created_at
AND us.first_post_created_at BETWEEN :start_date::date AND NOW()
ORDER BY us.first_post_created_at desc
This is a minor modification of this query by @tshenry:
It could be improved by having a set time which it looks back from, e.g. one week or one month - but this defeated me as I couldn’t work out how to get NOW() - 7 or the like to work.
The post notices are actually stored in the post_custom_fields table, so you can get a more precise list of posts like this:
-- int :days_ago = 7
p.id AS post_id,
pcf.value AS "notice type"
FROM post_custom_fields pcf
INNER JOIN posts p ON pcf.post_id = p.id
INNER JOIN topics t ON p.topic_id = t.id
WHERE pcf.name = 'notice_type'
AND p.created_at > NOW() - INTERVAL ':days_ago days'
AND t.archetype = 'regular'
ORDER BY p.created_at ASC