CREATE TABLE orders (customer_id VARCHAR)
CREATE TABLE customers (customer_name VARCHAR, customer_id VARCHAR)

What is the name of the customer who has the most orders?
SELECT T1.customer_name FROM customers AS T1 JOIN orders AS T2 ON T1.customer_id = T2.customer_id GROUP BY T1.customer_id ORDER BY COUNT(*) DESC LIMIT 1
SELECT "T1"."customer_name" FROM "customers" AS "T1" JOIN "orders" AS "T2" ON "T1"."customer_id" = "T2"."customer_id" GROUP BY "T1"."customer_id" ORDER BY COUNT(*) DESC NULLS LAST LIMIT 1