Please show me all customers and their contact channels | Do you want the names of customers or id? | names please
SELECT DISTINCT customer_name, channel_code FROM customers AS t1 JOIN customer_contact_channels AS t2 ON t1.customer_id   =   t2.customer_id
all customers and their contact channels refers to SELECT DISTINCT customer_name, channel_code; names of customers refers to customer_name; joining customers with their contact channels refers to JOIN on customer_id.