Patient Gender Percentage Query | Dataford Interview Questions

Your question is Patient Gender Percentage Query. Start with the requirements and the two tables on the right.

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Problem

Exusia Clinical Data Hub needs a basic demographic quality metric for its registered patient population. Write a PostgreSQL query that calculates the percentage of all registered patients whose recorded gender is M.

Requirements

Include every patient in the denominator, including patients without a demographics row or with a NULL gender.
Count each patient at most once, even if the demographics table contains duplicate records.
Return one row with the percentage in percent form, rounded to the nearest hundredth, such as 40.00 for 40 percent.
Avoid division-by-zero errors if the patient table is empty.

Schema

patients

Column	Type	Description
patient_idPK	INTEGER	Unique registered patient identifier
patient_name	VARCHAR(100)	Patient display name

patient_demographics

Column	Type	Description
demographic_idPK	INTEGER	Unique demographics record identifier
patient_id	INTEGER	Referenced patient identifier
gender	VARCHAR(20)	Recorded gender value