Question

I will create frienship system for my project. I couldn’t decide whether I should store friends in a column at user’s row or create a friends table and store there with user IDs? To clearify which usage is better:

Should users table be like this?

+-----------+-----------+---------------+
+    id     + username  +    friends    +
+-----------+-----------+---------------+
+    11     + user_x    + 12;23;15;3;7  +
+-----------+-----------+---------------+

with

<?php explode(';',$friends); ?>

or;
Sould I create a friends table like this?

+-----------+-----------+---------------+
+    id     +   user    +     friend    +
+-----------+-----------+---------------+
+    1      +    11     +       12      +
+-----------+-----------+---------------+
+    2      +    11     +       23      +
+-----------+-----------+---------------+
+    3      +    11     +       15      +
+-----------+-----------+---------------+
+    4      +    11     +       3       +
+-----------+-----------+---------------+
+    5      +    11     +       7       +
+-----------+-----------+---------------+

with

SELECT friend FROM friends WHERE user = 11

Which one is better? Thank you

Answer 1

The second is lot more flexible, for example, it makes it easy for you to query for ‘people who have friended you’. Unfriending simply involves deleting a single row rather than manipulating a string. You can easy generate stats on how many friends people have, etc…

You can still achieve the effect of the first option if that’s important for you. Simply use GROUP_CONCAT to get all the friend ids in a list, e.g.

 SELECT id,foo,bar,GROUP_CONCAT(friend_id) as friends 
 FROM user 
 LEFT JOIN friends ON(user.id=friends.user)
 GROUP BY user.id;