Finding Min and Max per Country

Question

Im trying to find the distributor with the highest and lowest quantity for each country in two columns distributor with minimum quantity and maximum quantity I have been able to get the information from other posts but it is in a column however I want it on a row per country

See http://sqlfiddle.com/#!17/448f6/2

Desired result

"country"   "min_qty_name"  "max_qty_name"
1. "Madagascar" "Leonard Cardenas" "Gwendolyn Mccarty"
2. "Malaysia"   "Arsenio Knowles" "Yael Carter" 
3. "Palau"      "Brittany Burris" "Clark Weaver"  
4. "Tanzania"   "Levi Douglas" "Levi Douglas"

Answer 1

You can use subqueries:

select distinct country,
(select distributor_name 
 from product 
 where country = p.country 
 order by quantity limit 1) as min_qty_name,
 (select distributor_name 
 from product 
 where country = p.country 
 order by quantity desc limit 1) as max_qty_name
 from product p;

Fiddle

Answer 2

You can do it with cte too ( result here )

WITH max_table AS
(      
    SELECT ROW_NUMBER() OVER (partition by country order by country,quantity DESC) AS rank,
    country, quantity,distributor_name
    FROM
    product
),
min_table AS
(      
    SELECT ROW_NUMBER() OVER (partition by country order by country,quantity) AS rank,
    country, quantity,distributor_name
    FROM
    product
)
SELECT m1.country,m2.distributor_name,m1.distributor_name
from max_table m1, min_table m2
where m1.country = m2.country
and m1.rank = 1 and m2.rank = 1

Answer 3

You can do this with a single sort and pass through the data as follows:

with min_max as (
  select distinct country, 
         first_value(distributor_name) over w as min_qty_name,
         last_value(distributor_name) over w as max_qty_name
    from product
  window w as (partition by country 
                   order by quantity
            rows between unbounded preceding
                     and unbounded following)
)
select * 
  from min_max
 order by min_max;

Updated Fiddle