I've done threaded comments with adjacency lists like this in MySQL in the past, and it worked well. Note also that it's compatible with scores moving siblings

I've done threaded comments with adjacency lists like this in MySQL in the past, and it worked well. Note also that it's compatible with scores moving siblings around relative to one another -- just calculate sibling position based on both score and date. Your schema might look something like this: id, date, topic_id, parent_id, score, payload