CREATE TABLE customers (customer_name VARCHAR2, customer_id VARCHAR2)
CREATE TABLE mailshot_customers (customer_id VARCHAR2)

Show the names of customers who have the most mailshots.
SELECT T2.customer_name FROM mailshot_customers AS T1 JOIN customers AS T2 ON T1.customer_id = T2.customer_id GROUP BY T1.customer_id ORDER BY COUNT(*) DESC LIMIT 1
SELECT "T2"."customer_name" FROM "mailshot_customers" "T1" JOIN "customers" "T2" ON "T1"."customer_id" = "T2"."customer_id" GROUP BY "T1"."customer_id" ORDER BY COUNT(*) DESC FETCH FIRST 1 ROWS ONLY