List the names of all the customers that use email as a contact channel and the date they became a member.
SELECT t1.customer_name, t1.date_became_customer FROM customers AS t1 JOIN customer_contact_channels AS t2 ON t1.customer_id   =   t2.customer_id WHERE t2.channel_code   =   'Email'
customers that use email as a contact channel refers to WHERE channel_code = 'Email'; date they became a member refers to date_became_customer;