SQL: Week-over-Week Call Growth | Dataford Interview Questions

Your question is SQL: Week-over-Week Call Growth. Start with the requirements and the two tables on the right.

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Problem

Doximity’s analytics team wants to monitor weekly call volume for Doximity Dialer. Write a PostgreSQL query that calculates completed telemedicine call volume and its week-over-week growth rate.

Requirements

Count only calls with status = 'completed' and a non-null started_at.
Include every week in calendar_weeks, including weeks with zero completed calls.
Compare each week with the immediately preceding week. Return NULL for the first week and whenever the prior week has zero calls.
Return results in chronological order, with growth expressed as a percentage rounded to two decimal places.

Schema

telemedicine_calls

Column	Type	Description
call_idPK	INTEGER	Unique telemedicine call identifier
started_at	TIMESTAMP	Timestamp when the call started
status	VARCHAR(20)	Call outcome, such as completed or missed

calendar_weeks

Column	Type	Description
week_startPK	DATE	Monday that begins the reporting week