A customer who places a second order within 30 days of their first is far more likely to stick around. Find them.
Return name, first_order, second_order (dates) and days_between (a whole number of days) for every customer whose second order was within 30 days (inclusive) of their first. Sort by days_between, then name.
Schema
customers(id, name, country, signup_date)
orders(id, customer_id, order_date, total)