SQL for Average Length of Stay | Dataford Interview Questions

Write a SQL query to find the average length of stay for patients in a specific department.

Use the provided patient, department, and admission data. Calculate length of stay in days using completed admissions only, and filter the result to the Cardiology department.

Output

Return one row for the Cardiology department.
Include department_name and average_length_of_stay_days.
Round the average to two decimal places.

Schema

patients

Column	Type	Description
patient_idPK	INT	Unique patient identifier
first_name	VARCHAR(50)	Patient first name
last_name	VARCHAR(50)	Patient last name

departments

Column	Type	Description
department_idPK	INT	Unique department identifier
department_name	VARCHAR(100)	Hospital department name

admissions

Column	Type	Description
admission_idPK	INT	Unique admission identifier
patient_id	INT	Admitted patient identifier
department_id	INT	Department responsible for the admission
admitted_at	TIMESTAMP	Admission date and time
discharge_at	TIMESTAMP	Discharge date and time, null for an ongoing admission

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Problem