array in MySQL

Question

I want to store an array in a record.

Table1:

ID, Name, Friends (friends should be an array)
1, Bill, 2&3
2, Charles, 1&3
3, Clare, 1

I want to be able to do a search like this:

SELECT * FROM Table1 WHERE Friends='3'

to find everyone who has Clare listed as a friend

Answer 1

You might want a comma-separated value, but it's not recommended. Why not use another table for showing relationships?

Table2
----------------------
PARENT_ID | FRIEND_ID
----------------------
1         | 2
1         | 3
2         | 1
2         | 3
----------------------

Answer 2

Unless you have a really good reason for doing this, you should keep your data normalized and store the relationships in a different table. I think perhaps what you are looking for is this:

CREATE TABLE people (
    id int not null auto_increment,
    name varchar(250) not null,
    primary key(id)
);

CREATE TABLE friendships (
    id int not null auto_increment,
    user_id int not null,
    friend_id int not null,
    primary key(id)
);

INSERT INTO people (name) VALUES ('Bill'),('Charles'),('Clare');

INSERT INTO friendships (user_id, friend_id) VALUES (1,3), (2,3);

SELECT *
  FROM people p
    INNER JOIN friendships f
      ON f.user_id = p.id
  WHERE f.friend_id = 3;

+----+---------+----+---------+-----------+
| id | name    | id | user_id | friend_id |
+----+---------+----+---------+-----------+
|  1 | Bill    |  1 |       1 |         3 |
|  2 | Charles |  2 |       2 |         3 |
+----+---------+----+---------+-----------+
2 rows in set (0.00 sec)

Answer 3

This looks like the perfect place for a relation table instead: Table 1:

ID, Name
1,  Bill
2,  Charles
3, Clare

Table 2 (the relation table)

ID, FriendID
1,  2
1,  3
2,  1
2,  3
3,  1

The second table keeps track of the friend relations by connecting ID's from Table1.