Exploding in php - php

Question

In my table 'users' there are 'friends' ,
Like this :
+----+------+---------+
| id | name | friends |
+----+------+---------+
| 1 | a | 0,1,2 |
| 2 | b | 0,1,3 |
| 3 | c | 0,1 |
+----+------+---------+
How do I use the explode function to get the friends id one by one (not 0,1,2) that are separated by a comma (,) ;
How do I select the id? (Example) :
$sql = Select id from users where id = (exploded)
if (mysql_num_rows($sql) > 0 ) {
$TPL->addbutton('Unfriend');
}else{
$TPL->addbutton('Add as Friend')
}

Answer 1

The solution here is actually a slight change in your database structure. I recommend you create a "many-to-many" relational table containing all of the users friends referenced by user.
+---------+-----------+
| user_id | firend_id |
+---------+-----------+
| 1 | 2 |
| 1 | 3 |
| 1 | 4 |
| 2 | 1 |
| 2 | 5 |
+---------+-----------+
If you are storing lists of values within one field then that is the first sign that your database design is not quite optimal. If you need to search for a numerical value, it'll always be better to place an index on that field to increase efficiency and make the database work for you and not the other way around :)
Then to find out if a user is a friend of someone, you'll query this table -
SELECT * FROM users_friends WHERE
`user_id` = CURRENT_USER AND `friend_id` = OTHER_USER
To get all the friends of a certain user you would do this -
SELECT * FROM users_friends WHERE `user_id` = CURRENT_USER

Answer 2

Just a simple example that will make you clear how to proceed:
// Obtain an array of single values from data like "1,2,3"...
$friends = explode(',', $row['friends']);
Then, back in your query:
// Obtain back data like "1,2,3" from an array of single values...
$frieldslist = implode(',', $friends);
$sql = "SELECT * FROM users WHERE id IN ('" . $frieldslist . "')";

Answer 3

to get an array of if ids from your string explode would be used like this
$my_array = explode("," , $friends);
but you'd probably be better using the mysql IN clause
$sql = "Select id from users where id in (".$row['friends'].")";

Answer 4

Just a quick idea. Change your database's table. It is certain that after a while many problems will arise.
You could have something like this.
id hasfriend
1 2
1 3
2 1 no need to be here (You have this already)
2 4
.....
You can do this by using indexes for uniqueness or programming. You may think of something better. Change your approach to the problem to something like this.