Table schema:
CREATE TABLE customers (phone_number VARCHAR, customer_id VARCHAR); CREATE TABLE complaints (customer_id VARCHAR, date_complaint_raised VARCHAR)

Question: What is the phone number of the customer who has filed the most recent complaint?
SQL: SELECT t1.phone_number FROM customers AS t1 JOIN complaints AS t2 ON t1.customer_id = t2.customer_id ORDER BY t2.date_complaint_raised DESC LIMIT 1