SQL: DAU/MAU Ratio | Dataford Interview Questions

Meta's Product Growth team uses the AARRR funnel to monitor activation and retention across Instagram Reels, Facebook Groups, and Instagram Save activity. Write a PostgreSQL query that calculates the daily DAU/MAU ratio for the fixed 30-day period from 2025-03-01 through 2025-03-30.

Requirements

Count distinct active users with at least one valid activity event per calendar day as dau.
Count distinct active users with activity during the trailing 30-day period ending on each calendar day as mau.
Return every calendar date in the reporting window, including dates with zero DAU.
Calculate dau_mau_ratio as DAU divided by MAU, rounded to four decimal places. Avoid division by zero.

Schema

users

Column	Type	Description
user_idPK	VARCHAR(20)	Meta user identifier
account_status	VARCHAR(20)	Current account state
signup_date	DATE	Account creation date

app_activity_events

Column	Type	Description
event_idPK	INT	Unique activity event identifier
user_id	VARCHAR(20)	User associated with the event
event_date	DATE	Calendar date of the event
surface	VARCHAR(30)	Meta product surface
event_name	VARCHAR(30)	Recorded activity type

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