Prime Next-Month Cohort Retention

SQL practice question · Hard · Analytics · Amazon

Amazon wants to know how many new Prime members come back the very next month. Group members into cohorts by the calendar month of `signup_date`. A member is *retained* if they placed at least one order in the calendar month immediately after their signup month (orders in the signup month itself, or two or more months later, do not count; several orders count once). Return `cohort_month` ('YYYY-MM'), `cohort_size`, `retained_m1`, `retention_pct` = ROUND(100.0 * retained_m1 / cohort_size, 1). Every cohort must appear, even if nobody was retained. Order by `cohort_month`.

Table: prime_signups

Schema of prime_signups
ColumnType
customer_idINTEGER
signup_dateDATE
Sample rows of prime_signups
customer_idsignup_date
12026-01-05
22026-01-20
32026-01-28
42026-02-02
52026-02-14
62026-03-03

Table: prime_orders

Schema of prime_orders
ColumnType
order_idINTEGER
customer_idINTEGER
order_dateDATE
Sample rows of prime_orders
order_idcustomer_idorder_date
10112026-01-06
10212026-02-10
10322026-02-01
10422026-02-15
10532026-03-05
10642026-03-01
10752026-02-20
10862026-04-30
Expected output on the sample data
cohort_monthcohort_sizeretained_m1retention_pct
2026-013266.7
2026-022150
2026-0311100

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