SQL AWS Athena Group by Without a Column

Question

I have this dataset

patient_id   doctor_id   status   created_at
1            1           A        2020-10-01 10:00:00
1            1           P        2020-10-01 10:30:00
1            1           U        2020-10-01 10:35:00
1            2           A        2020-10-01 10:40:00
...

I want to group it by patient_id and doctor_id but without the status is grouped so the result will be like this

patient_id   doctor_id   status   created_at
1            1           U        2020-10-01 10:35:00
1            2           A        2020-10-01 10:40:00
...

AWS Athena have to grouped all column but I need the last status

Answer 1

In Athena/Presto you can do this with themax_by function:

SELECT
  patient_id,
  doctor_id,
  MAX_BY(status, created_at) AS last_status
FROM the_table
GROUP BY 1, 2

max_by(x, y) function returns the value of the column x for the row with the max value of column y of the group.

Answer 2

ROW_NUMBER provides one option here:

WITH cte AS (
    SELECT *,
        ROW_NUMBER() OVER (PARTITION BY patient_id, doctor_id ORDER BY created_at DESC) rn
    FROM yourTable
)

SELECT patient_id, doctor_id, status, created_at
FROM cte
WHERE rn = 1
ORDER BY patient_id, doctor_id;