CREATE TABLE complaints (customer_id VARCHAR, date_complaint_raised VARCHAR)
CREATE TABLE customers (phone_number VARCHAR, customer_id VARCHAR)

What is the phone number of the customer who has filed the most recent complaint?
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
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 NULLS LAST LIMIT 1