query: SELECT avg(active_to_date - active_from_date) FROM customer_contact_channels
question: Compute the average active time span of contact channels.
query_toks: SELECT avg ( active_to_date - active_from_date ) FROM customer_contact_channels
query_toks_no_value: select avg ( active_to_date - active_from_date ) from customer_contact_channels
question_toks: Compute the average active time span of contact channels.