SQL
MediaAttachment.where.not(remote_url: '').where('created_at < ?', 1.week.ago).where('NOT EXISTS (SELECT 1 FROM statuses AS reblogs WHERE reblogs.id = media_attachments.status_id AND reblogs.created_at >= ? LIMIT 1)', 1.week.ago).count
D, [2017-07-13T11:12:34.223311 #1214] DEBUG -- : (3345.8ms) 略
=> 61722