如何在MySQL查询中获取GROUP BY的最新索引？

Question

I got confused about the algorithm and way to get the latest index of Group by. I have a query like this.

SELECT hasil_kmbg AS RESULT,
   EXTRACT(MONTH
           FROM tgl_check) AS MONTH,
   EXTRACT(YEAR
           FROM tgl_check) AS YEAR
FROM perkembangan
WHERE no_pasien=11
GROUP BY MONTH,
         id_kmbg DESC

and here is result of the query

|Result|Month|Year|
-------------------
|3     |1    |2013|
|1     |1    |2013|
|5     |1    |2013|
|1     |2    |2013|
|1     |3    |2013|
and so on

the question is, how I just get Result which is Result is 3 in Month 1? I didn't want to show other result int Month 1 except 3 (the latest, I order it by desc).

Answer 1

You are getting multiple rows per month because you have included id_kmbg in the group by clause. I think you want the max() function:

select max(hasil_kmbg) as Result, EXTRACT(MONTH FROM tgl_check) as Month,
       EXTRACT(YEAR FROM tgl_check) as Year
from perkembangan
where no_pasien=11
group by Month, Year;

Answer 2

I think that you are looking for this:

SELECT hasil_kmbg AS RESULT,
       EXTRACT(MONTH
               FROM tgl_check) AS MONTH,
       EXTRACT(YEAR
               FROM tgl_check) AS YEAR
FROM perkembangan
WHERE no_pasien=11
ORDER BY id_kmbg DESC
LIMIT 1

My hunch is that you don't need the GROUP BY here (since you are ordering by ID DESC).

If you need a group by, you might need to rework how you select hasil_kmbg.