Question

So I got this statement, which works fine:

SELECT   MAX(patient_history_date_bio) AS med_date, medication_name
FROM     biological
WHERE    patient_id = 12)
GROUP BY medication_name

But, I would like to have the corresponding medication_dose also. So I type this up

SELECT   MAX(patient_history_date_bio) AS med_date, medication_name, medication_dose
FROM     biological
WHERE    (patient_id = 12)
GROUP BY medication_name

But, it gives me an error saying:

“coumn ‘biological.medication_dose’ is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.”.

So I try adding medication_dose to the GROUP BY clause, but then it gives me extra rows that I don’t want.
I would like to get the latest row for each medication in my table. (The latest row is determined by the max function, getting the latest date).

How do I fix this problem?

Answer 1

Use:

SELECT b.medication_name,
       b.patient_history_date_bio AS med_date,
       b.medication_dose
  FROM BIOLOGICAL b
  JOIN (SELECT y.medication_name,
               MAX(y.patient_history_date_bio) AS max_date
          FROM BIOLOGICAL y
      GROUP BY y.medication_name) x ON x.medication_name = b.medication_name
                                   AND x.max_date = b.patient_history_date_bio
 WHERE b.patient_id = ?