Question

I’m trying to create a separate table that would track read/unread posts. Using MySQLi I will have two tables items and items_tracking. When the page is rendered it will join the the tables and check if the user read the posts or not.

items
+-------+------------+----+
|  id   | created_by | .. |
+-------+------------+----+
| item1 | id12       | .. |
| item2 | id433      | .. |
+-------+------------+----+

items_tracking
+---------+---------+------+
| user_id | item_id | read |
+---------+---------+------+
| id1     | item1   |    0 |
| id2     | item2   |    0 |
| id94    | item1   |    1 |
+---------+---------+------+

Now the idea was that whenever a new item/post is created in the items table, it will also create rows in the items_tracking table for all users and with column read = 0. Problem is, I have no idea how to work around this since the foreign key I would use in items_tracking is still pretty much undetermined.

Any ideas on how to approach inserting in both tables at the same time, while the second table references the first?

Answer 1

You don’t need records with read=0 in the tracking table.

SELECT ..., t.read FROM items i LEFT JOIN items_tracking t ON (t.item_id = i.id)

This query will work even if there is no corresponding record in items_tracking; in this case, t.read in the result will be NULL. You only need to insert the records with read = 1, although you don’t need even this flag, you test for t.item_id IS NOT NULL to see if you have a record in items_tracking.