MySQL How to select friends from a friendship table?

Question

Hi I have a simple database for storing friendship, with just two columns person_a, person_b , denoting that person_a and person_b are friends. From a big list like this what query should I run to get say get all friends of 'sam'. Thank you.

Answer 1

Use a UNION:

SELECT person_b
FROM friendship
WHERE person_a = 'sam'
UNION
SELECT person_a
FROM friendship
WHERE person_b = 'sam'

Answer 2

You might want to try something like

SELECT  *
FROM    users u INNER JOIN
        (
            SELECT  CASE
                        WHEN person_a = yourid THEN
                            person_b
                        ELSE person_a
                    END person_id
            FROM    FRIENDSHIPS
            WHERE   person_a = yourid
            OR      person_b = yourid
        ) myFriends ON u.userID = myFriends.person_id

Answer 3

May be try like this,

SELECT person_a, person_b
FROM friendship
WHERE person_a = 'sam' or person_b = 'sam'

Use the query like this, after that 

if(person_a=='sam') {
   $frnd = $rowfetch["person_b"];
} else if(person_b=='sam') {
   $frnd = $rowfetch["person_a"];
}

Answer 4

refer to my post here

http://stackoverflow.com/questions/2542800/how-to-make-an-add-friend-defriend-function-in-php/2542842#2542842