The results set for problem #2 in our SQL coding challenge.

gistfile1.txt

+----------------+-------+---------------------+---------------------+
| sender_user_id | name  | num_users_contacted | num_users_responded |
+----------------+-------+---------------------+---------------------+
|              3 | Greg  |                   1 |                   1 |
|              1 | John  |                   4 |                   0 |
|              7 | Linda |                   1 |                   1 |
|              6 | Sue   |                   2 |                   2 |
+----------------+-------+---------------------+---------------------+

select * from (
select sender_user_id, count(distinct recipient_user_id) as ColdMessages from (
select i1.id,i1.sender_user_id,i1.recipient_user_id,created_at, 1 as ColdFlag from internal_messages i1 where i1.sender_user_id not in (select distinct i2.recipient_user_id from internal_messages i2 where i2.created_at<=i1.created_at and i1.recipient_user_id=i2.sender_user_id )) t1
group by sender_user_id ) temp1

left join

(select count(distinct sender_user_id) as Responded,recipient_user_id from
(
select distinct t2.id,t2.sender_user_id,t2.recipient_user_id from
(select i1.id,i1.sender_user_id,i1.recipient_user_id,created_at, 1 as ColdFlag from internal_messages i1 where i1.sender_user_id not in (select distinct i2.recipient_user_id from internal_messages i2 where i2.created_at<=i1.created_at and i1.recipient_user_id=i2.sender_user_id ))t1 inner join
internal_messages t2 on t2.sender_user_id=t1.recipient_user_id where t2.created_at>t1.created_at) t3 group by recipient_user_id ) temp2

on temp1.sender_user_id=temp2.recipient_user_id