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

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ASP.NET

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SQL-Server

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?