Person with the most friends

Table request_accepted:

Each row is one accepted friend request, which makes the two people friends. A pair appears at most once, in one direction only. A person's friends can come from either column.

Find the person with the most friends. If several people tie, return all of them.

Output columns: id, num (number of friends).

CREATE TABLE request_accepted (
  requester_id int NOT NULL,
  accepter_id int NOT NULL,
  PRIMARY KEY (requester_id, accepter_id)
);