Determining unread items in a forum

Question

Using PHP and MySQL, I have a forum system I\'m trying to build. What I want to know is, how can I set it so that when a user reads a forum entry, it shows as read JUST for

Answer 1

May be storing in another table UserID,threadID, LastReadDateTime when the user read that thread.

if (LastPostDateTime > LastReadDateTime) you got an unread post.

Sadly you have a great overhead, on every read you'll have a write.