id| username| country | privacy
1 | Everest | Austria | 0
2 | Mark    | Sweden  | 0
3 | Precious| Norway  | 1
4 | Daniel  | Ghana   | 1
5 | Jim     | Greece  | 1
6 | Ayo     | Brazil  | 0

id| sender_id| receiver_id| accepted
1 | 1        | 3          | 0
2 | 3        | 4          | 0

id| username| country | privacy
2 | Mark    | Sweden  | 0
6 | Ayo     | Brazil  | 0

SELECT *
FROM users
WHERE privacy = 0
AND id <> 3
AND id NOT IN (
    SELECT receiver_id FROM friends WHERE sender_id   = 3
    UNION ALL
    SELECT sender_id   FROM friends WHERE receiver_id = 3
)

SELECT Users.*
from Users
left join Friends on (users.id = Friends.senderId and Friends.senderId is null)