Get highest value ID - sql

Question

I need to print the Region ID and the count of countries he holds, but only for the highest one.
My table is like this:
COUNTRY_ID COUNTRY_NAME REGION_ID
AR Argentina 2
AU Belgium 3
BE Brazil 1
BR Canada 2
CA Switzerland 2
CN China 1
DE Germany 3
And the result must be something like:
REGION_ID Quantity
2 3

Answer 1

You can use below sql for that purpose.
I use row_number analytic function to rank the rows after being grouped by REGION_ID column. Then, I filter by rnb = 1 to get the row with maximun quantity.
select REGION_ID, QUANTITY
from (
select t.REGION_ID, count(*)quantity, row_number()over(order by count(*) desc) rnb
from YourTable t
group by t.REGION_ID
)
where rnb = 1
demo

Answer 2

From Oracle 12c, you can use:
SELECT region_id,
COUNT(*) AS quantity
FROM table_name
GROUP BY region_id
ORDER BY quantity DESC
FETCH FIRST ROW ONLY;
Before that:
SELECT *
FROM (
SELECT REGION_ID,
COUNT(*) AS quantity
FROM table_name
GROUP BY region_id
ORDER BY quantity DESC
)
WHERE ROWNUM = 1;
Which, for your sample data:
CREATE TABLE table_name (COUNTRY_ID, COUNTRY_NAME, REGION_ID) AS
SELECT 'AR', 'Argentina', 2 FROM DUAL UNION ALL
SELECT 'AU', 'Belgium', 3 FROM DUAL UNION ALL
SELECT 'BE', 'Brazil', 1 FROM DUAL UNION ALL
SELECT 'BR', 'Canada', 2 FROM DUAL UNION ALL
SELECT 'CA', 'Switzerland', 2 FROM DUAL UNION ALL
SELECT 'CN', 'China', 1 FROM DUAL UNION ALL
SELECT 'DE', 'Germany', 3 FROM DUAL;
Both output:
REGION_ID
QUANTITY
2
3
db<>fiddle here

Answer 3

In Oracle you may nest aggregate functions to calculate total on group by result. So you may use last aggregate function to get highest id:
select
max(region_id) keep(
dense_rank last
/*
region_id for highest count(*)
calculated per region_id
*/
order by count(*) asc
) as region_id,
max(count(*)) as quantity
from table_name
group by region_id
REGION_ID | QUANTITY
--------: | -------:
2 | 3
db<>fiddle here