CREATE TABLE customer_addresses (customer_id VARCHAR, address_id VARCHAR)
CREATE TABLE customers (customer_id VARCHAR)
CREATE TABLE addresses (city VARCHAR, address_id VARCHAR)

Which city has the most customers living in?
SELECT t3.city FROM customers AS t1 JOIN customer_addresses AS t2 ON t1.customer_id = t2.customer_id JOIN addresses AS t3 ON t2.address_id = t3.address_id GROUP BY t3.city ORDER BY COUNT(*) DESC LIMIT 1
SELECT "t3"."city" FROM "customers" AS "t1" JOIN "customer_addresses" AS "t2" ON "t1"."customer_id" = "t2"."customer_id" JOIN "addresses" AS "t3" ON "t2"."address_id" = "t3"."address_id" GROUP BY "t3"."city" ORDER BY COUNT(*) DESC NULLS LAST LIMIT 1