How do forums show you unread topics?

Question

I have user discussion forums I coded in php/mysql, I am wanting to know how the big name forums can make it show you which topics have new posts in them, usually by changin

Answer 1

You could have a table that gets an insert whenever a thread gets read, if the user reading it hasn't already. Then when someone adds to the thread you can delete all entries in the table for that thread, thus making it unread for all users.

The table structure would be something like

forum_id thread_id user_id

With the optional extra has_read_id for your primary key, with the other fields making a composite key.