Tell me the active duration for each customer contact channel.
select active_to_date - active_from_date from customer_contact_channels
Among them, what is the longest active duration?
select active_to_date - active_from_date from customer_contact_channels order by (active_to_date - active_from_date) desc limit 1
What is the channel code and contact number of the customer contact channel whose active duration was the longest
select channel_code, contact_number from customer_contact_channels where active_to_date - active_from_date = (select active_to_date - active_from_date from customer_contact_channels order by (active_to_date - active_from_date) desc limit 1)