How to structure database for unread item alerts per user - php

Question

I just have a general database theory question. I have a need to make something similar to showing what posts/items a user has viewed or not (such as in a forum) or an unread email message. What I have is there are posts that multiple users can view, but it needs to separate by user who has actually viewed it. So if User A viewed Post 1, it would no longer show that Post 1 is a new item to view, but to User B, it would still show that Post 1 is a new item to view.
I've search for other ideas and one of them is to get a timestamp of when the user last logged in, but I actually need to keep track of the posts they've seen as opposed to posts that have happened since they last logged in.
I would like a MySQL database solution if possible, but I'm open to cookies if that is a must. I could do this on my own and just figure it out, but I'd appreciate any advice on how to properly structure a table(s) to make this the most efficient. Also, bandwidth and storage is not issue.

Answer 1

While reviewing the relevant schema for phpBB, I found the following:
# Table: 'phpbb_topics_track'
CREATE TABLE phpbb_topics_track (
user_id mediumint(8) UNSIGNED DEFAULT '0' NOT NULL,
topic_id mediumint(8) UNSIGNED DEFAULT '0' NOT NULL,
forum_id mediumint(8) UNSIGNED DEFAULT '0' NOT NULL,
mark_time int(11) UNSIGNED DEFAULT '0' NOT NULL,
PRIMARY KEY (user_id, topic_id),
KEY topic_id (topic_id),
KEY forum_id (forum_id)
) CHARACTER SET `utf8` COLLATE `utf8_bin`;
And:
# Table: 'phpbb_forums_track'
CREATE TABLE phpbb_forums_track (
user_id mediumint(8) UNSIGNED DEFAULT '0' NOT NULL,
forum_id mediumint(8) UNSIGNED DEFAULT '0' NOT NULL,
mark_time int(11) UNSIGNED DEFAULT '0' NOT NULL,
PRIMARY KEY (user_id, forum_id)
) CHARACTER SET `utf8` COLLATE `utf8_bin`;
Then I look here in their wiki:
This table keeps record for visited topics in order to mark them as
read or unread. We use the mark_time timestamp in conjunction with
last post of topic x's timestamp to know if topic x is read or not.
In order to accurately tell whether a topic is read, one has to also
check phpbb_forums_track.
So essentially they have a lookup table to store the data associated with a user's viewing of a topic (thread), and then check it against the timestamp in the forum view table, to determine whether the topic has been viewed by the user.

Answer 2

Just create a simple cross-reference table (read_posts or something):
user_id|post_id
----------------
2 | 132
53 | 43
....
Make sure that both of these columns are indexed (especially important that the user_id be indexed) and then use a join (or a sub-query) to select unread posts for the logged in user. If you're just trying to show a list of unread posts, for example, you just run:
SELECT * FROM `posts` WHERE `post_id` NOT IN (
SELECT `post_id` FROM `read_posts` WHERE `user_id`='[$USER ID]')
ORDER BY [your ordering clause]

Answer 3

Based on this description I would use a simple table with maybe 3 columns.
User ID
Post ID
Timestamp First Viewed
When a user views a post, add a row to the table. If a row does not exist in the table for a given user/post id combo, then they have not viewed the post.