Dashers Week-Over-Week Retention SQL | Dataford Interview Questions

Write a SQL query to calculate the retention rate of Dashers week-over-week.

Use the dashers and dasher_deliveries tables. A Dasher is active in a week if they completed at least one delivery during that week.

Output

One row per week that follows a week with active Dashers
Columns: week_start, retained_dashers, prior_week_dashers, and retention_rate_pct
Include Dashers active in the prior week in the denominator, and Dashers active in both weeks in the numerator
Round the retention rate to two decimal places and order by week_start ascending

dashers

Column	Type	Description
dasher_idPK	INT	Unique identifier for a Dasher
signup_date	DATE	Date the Dasher signed up
is_active	BOOLEAN	Whether the Dasher account is currently active

dasher_deliveries

Column	Type	Description
delivery_idPK	INT	Unique identifier for a delivery
dasher_id	INT	Dasher who handled the delivery
delivery_date	DATE	Date the delivery was completed or attempted
status	VARCHAR(20)	Delivery status, such as completed or cancelled

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