How do i select a max of a sum with multiple tables

Question

I need some help with a problem. I am trying to get a max from a sum with three tables. I've been trying to figure it out with help from other post on here but so far none of them have helped me. I manage to get the right answer when using limit 1 but i was wondering how I can do it without that.

The three tables are

Tables

So far I got this

(select vnamn, sum(mangd) as a from land, export, varldsdel where varldsdel.vkod=land.vkod and land.landkod=export.landkod and ar=2004 group by vnamn)

this give me the following result

+----------------+-------------+
|     vnamn      | sum(mangd)  |
+----------------+-------------+
| sydamerika     |       61000 |
| noramerika     |       50000 |
| europa         |       1200  |
+----------------+-------------+

Now this is where I get stuck. I want to do a max of this result so that only "sydamerika | 61000" shows and I've been trying to do this all day but can't get the hang of it.

Thanks

Answer 1

since you already have the select query, you can do this instead;

Select vnamn, max(a) as mangd from (select vnamn, sum(mangd) as a from land, export, varldsdel where varldsdel.vkod=land.vkod and land.landkod=export.landkod and ar=2004 group by vnamn) k

Answer 2

You can use a Common Table Expression (CTE) and then filter out on the highest value using the MAX aggregation function:

WITH summed_mangd AS (
    SELECT vnamn, 
           SUM(mangd) AS total 
    FROM       land
    INNER JOIN export
            ON export.landkod = land.landkod
    INNER JOIN varldsdel 
            ON varldsdel.vkod = land.vkod 
    WHERE ar = 2004 
    GROUP BY vnamn
)
SELECT vnamn,
       total
FROM summed_mangd
WHERE total = (SELECT MAX(total) 
               FROM summed_mangd)