PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

602 Chapter 27 Building User Authentication and Personalization
Figure 27.10
The deletion script notifies the user of deleted bookmarks and
then displays the remaining bookmarks.
As in the add_bms.php script, after the changes to the database have been made, you display
the new bookmark list using get_user_urls() and display_user_urls().
Implementing Recommendations
Finally, you’re ready for the link recommender script, recommend.php.There are many
different ways you could approach recommendations.You should perform what we call a
“like minds” recommendation.That is, look for other users who have at least one bookmark
the same as your given user.The other bookmarks of those other users might
appeal to your given user as well.
The easiest way to implement this as an SQL query is to use subqueries.The first
subquery looks like this:
select distinct(b2.username)
from bookmark b1, bookmark b2
where b1.username='".$valid_user."'
and b1.username != b2.username
and b1.bm_URL = b2.bm_URL)
This query uses aliases to join the database table bookmark to itself—a strange but sometimes
useful concept. Imagine that you actually have two bookmark tables, one called b1
and one called b2. In b1, you look at the current user and his bookmarks. In the other
table, you look at the bookmarks of all the other users.You are looking for other users