In social network like Facebook or Twitter, people send friend requests and accept others' requests as well.

Table  request_accepted  holds the data of friend acceptance, while  requester_id  and  accepter_id  both are the id of a person.

| requester_id | accepter_id | accept_date|
|--------------|-------------|------------|
| 1            | 2           | 2016_06-03 |
| 1            | 3           | 2016-06-08 |
| 2            | 3           | 2016-06-08 |
| 3            | 4           | 2016-06-09 |

Write a query to find the the people who has most friends and the most friends number. For the sample data above, the result is:

| id | num |
|----|-----|
| 3  | 3   |

Note: It is guaranteed there is only 1 people having the most friends.The friend request could only been accepted once, which mean there is no multiple records with the same  requester_id and  accepter_id value.

Explanation:
The person with id '3' is a friend of people '1', '2' and '4', so he has 3 friends in total, which is the most number than any others.

Follow-up:

In the real world, multiple people could have the same most number of friends, can you find all these people in this case?

select id, count(id) num
from
(select requester_id as id from request_accepted
union all
select accepter_id from request_accepted) t    #set up "t" is very important, or there is error
group by id
order by num desc
limit 1;

If multiple people could have the same most number of friends:

select id, count(id) num
from
(select requester_id as id from request_accepted
union all
select accepter_id from request_accepted) t1
group by id
having num = (select max(num) from
(select id, count(id) num
from
(select requester_id as id from request_accepted
union all
select accepter_id from request_accepted) t1
group by id) t2);