SQL Window Function for Latest Reading | Dataford Interview Questions

Write a SQL query using window functions to identify the most recent clinical reading for each dialysis patient at Fresenius Medical Care North America.

Use the provided patient and clinical reading data. Return only dialysis patients with at least one reading, selecting the latest timestamp and using the reading ID to break timestamp ties.

Output

One row per dialysis patient with a matching reading.
Columns: patient_id, patient_name, reading_id, reading_type, reading_value, unit, and reading_timestamp.
Order by patient_id ascending.

Schema

patients

Column	Type	Description
patient_idPK	INT	Unique dialysis patient identifier
patient_name	VARCHAR(100)	Patient name
is_dialysis_patient	BOOLEAN	Whether the patient is currently identified as a dialysis patient

clinical_readings

Column	Type	Description
reading_idPK	INT	Unique clinical reading identifier
patient_id	INT	Patient associated with the reading
reading_type	VARCHAR(50)	Type of clinical measurement
reading_value	DECIMAL(8,2)	Recorded clinical measurement value
unit	VARCHAR(20)	Unit of measurement
reading_timestamp	TIMESTAMP	Timestamp when the reading was recorded

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