What is the "active to date" for each customer?
select active_to_date from customer_contact_channels
What is the latest "active to date" for each customer?
select max(active_to_date) from customer_contact_channels group by customer_id
Find that information for the customer named "Tillman Ernser".
select max(t2.active_to_date) from customers as t1 join customer_contact_channels as t2 on t1.customer_id = t2.customer_id where t1.customer_name = "Tillman Ernser"