Running Total of Daily Signups | Dataford Interview Questions

Your question is Running Total of Daily Signups. Start with the requirements and the three tables on the right.

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Problem

DeFiner wants a reliable daily signup trend for its analytics dashboard. Write a PostgreSQL query that reports daily signups during February 1 through February 10, 2025, including days with no qualifying signups.

Requirements

Count distinct users whose signup event occurred on each calendar day.
Exclude test users, deleted users, users without a recognized acquisition channel, duplicate signup events, and events outside the requested date range.
Calculate the previous day's signup count with LAG.
Calculate the cumulative signup total with a windowed SUM ordered by date.
Return one row per calendar day in ascending date order.

Schema

users

Column	Type	Description
user_idPK	INT	Unique DeFiner user identifier
created_at	TIMESTAMP	Account creation timestamp
channel_id	INT	Acquisition channel identifier
is_test	BOOLEAN	Whether the account is a test account
deleted_at	TIMESTAMP	Account deletion timestamp

signup_events

Column	Type	Description
event_idPK	INT	Unique event identifier
user_id	INT	User associated with the event
event_type	VARCHAR(30)	Tracked event name
occurred_at	TIMESTAMP	Timestamp when the event occurred

acquisition_channels

Column	Type	Description
channel_idPK	INT	Unique acquisition channel identifier
channel_name	VARCHAR(100)	Human-readable acquisition channel
is_active	BOOLEAN	Whether the channel is currently active