Many database rows vs one comma separated values row

Question

I'm creating a table for allowing website users to become friends. I'm trying to determine which is the best table design to store and return a user's friends. The goal is to have fast queries and not use up a lot of db space.

I have two options:

Have individual rows for each friendship.

+----+-------------+-------------------+
| ID | User_ID     | Friend_ID         |
+----+-------------+-------------------+
| 1  | 102         | 213               |
| 2  | 64          | 23                |
| 3  | 4           | 344               |
| 4  | 102         | 2                 |
| 5  | 102         | 90                |
| 6  | 64          | 88                |
+----+-------------+-------------------+

Or store all friends in one row as CSV

    +----+-------------+-------------------+
    | ID | User_ID     | Friend_ID         |
    +----+-------------+-------------------+
    | 1  | 102         | 213,44,34,67,8    |
    | 2  | 64          | 23,33,45,105      |
    +----+-------------+-------------------+

When retrieving friends I can create an array using explode() however deleting a user would be trickier.

Edit: For second method I would separate each id in array in php for functions such as counting and others.

Which method do you think is better?

Answer 1

First method is definitely better. It's what makes relational databases great :)

It will allow you to search for and group by much more specific criteria than the 2nd method.

Say you wanted to write a query so users could see who had them as a friend. The 2nd method would require you to use IN() and would be much slower than simply using JOINS.

Answer 2

The first method is better in just about every way. Not only will you utilize your DBs indexes to find records faster, it will make modification far far easier.