Database: department_store
Question: What are the distinct names of customers who have purchased a keyboard?
SQL: select distinct t1.customer_name from customers as t1 join customer_orders as t2 on t1.customer_id  =  t2.customer_id join order_items as t3 on t2.order_id  =  t3.order_id join products as t4 on t3.product_id  =  t4.product_id where t4.product_name  =  "keyboard"