Facebook like notifications tracking (DB Design) Triggers or T-SQL?

I am just trying to figure out how facebook's database is structured for tracking notifications.
 
Wont go much into complexity like facebook is. If we imagine a simple table structure for notificaitons
 
notifications (id, userid, update, time);
 
We can get the notifications of friends using

    SELECT `userid`, `update`, `time`
    FROM `notifications`
    WHERE `userid` IN 
    (... query for getting friends...)

 
However what should be the table structure to check out which notifications has been read and which hasn't ?
 

I dont know if this is the best way to do this, but since I got no ideas from anyone else, this is what I would be doing.
 

We have 2 tables
 

    notification
    -----------------
    id (pk)
    userid
    notification_type (for complexity like notifications for pictures, videos, apps etc.)
    notification
    time
 

    notificationsRead
    --------------------
    id (pk) (i dont think this field is required, anyways)
    lasttime_read
    userid

 
The idea is to select notifications from notifications table and join the notificationsRead table and check the last read notification and rows with ID > notificationid. And each time the notifications page is opened update the row from notificationsRead table.
 
The query for unread notifications I guess would be like this..
 

   SELECT `userid`, `notification`, `time` from `notifications` `notificationsRead`
    WHERE 
    `notifications`.`userid` IN ( ... query to get a list of friends ...) 
    AND 
    (`notifications`.`time` > (
        SELECT `notificationsRead`.`lasttime_read` FROM `notificationsRead` 
        WHERE `notificationsRead`.`userid` = ...$userid...
    ))

 
The query above is not checked.
 
Now my understanding is that when a notification is added, we need to find the users friends and insert all those rows(a notification per friend) in the notification table right ? If this is correct, then, what would be the best way to achieve this ?
 
Triggers?
Write T-SQL (sql query in server side) to Select all the friends and then use SQL bulk copy?