SQL help with MAX query - sql

Question

I have a table of countries named bbc(name, region, area, population, gdp)
I want a table with the region, name and population of the largest ( most populated) countries by region. So far i've tried this:
SELECT region, name, MAX(population)
FROM bbc
GROUP BY region
It gave me an error message : ORA-00979: Not a GROUP BY Expression
I tried to change to GROUP BY region, name, but it doesn't give me the right table

Answer 1

You can use analytics for queries like that:
SELECT name, region, population
FROM (SELECT region, name, population
, MAX(population) OVER (PARTITION BY region) maxpop
FROM bbc)
WHERE population = maxpop;
The inline view gives you a table that looks like your base table, plus an extra column with the max population for the region. Your top-level select gives you the country, region and population of the largest country in each region.
To illustrate with a limited example:
SELECT * FROM bbc;
REGION NAME POPULATION
--------------- ------- ----------
North America USA 300000000
North America Canada 100000000
North America Mexico 50000000
South America Brazil 50000000
South America Argentina 40000000
South America Venezuela 20000000
Add the analytic function:
SELECT region, NAME, population
, MAX(population) OVER (PARTITION BY region) maxpop
FROM bbc;
REGION NAME POPULATION MAXPOP
--------------- ------- ---------- ----------
North America USA 300000000 300000000
North America Canada 100000000 300000000
North America Mexico 50000000 300000000
South America Brazil 50000000 50000000
South America Argentina 40000000 50000000
South America Venezuela 20000000 50000000
Then the finished product:
NAME REGION POPULATION
------- --------------- -----------
USA North America 300000000
Brazil South America 50000000
One more edit. You can avoid a nest select, but not a subquery:
SELECT NAME, region, population
FROM bbc
WHERE (region, population) IN
(SELECT region, MAX(population)
FROM bbc
group by region);

Answer 2

Here's the easiest and shortest way to do it, since Oracle has tuple testing, it can make the code shorter:
First, get the max population on each region:
SELECT region, MAX(population)
FROM bbc
GROUP BY region
Then test the countries against it:
select region, name, population
from bbc
where (region, population) in
(SELECT region, MAX(population)
FROM bbc
GROUP BY region)
order by region
If you want to support many RDBMS, use EXISTS:
select region, name, population
from bbc o
where exists
(SELECT null -- neutral. doesn't invoke Cargo Cult Programming ;-)
FROM bbc
WHERE region = o.region
GROUP BY region
HAVING o.population = MAX(population) )
order by region
Query tested here, both have similar output: http://sqlzoo.net/0.htm
http://www.ienablemuch.com/2010/05/why-is-exists-select-1-cargo-cult.html

Answer 3

In the vast majority of vases, the ORA-00979 error is caused because a non-aggregated column is not included in the GROUP BY clause. In this case you need to include name as well in your GROUP BY clause. Also, you should not be calling the MAX function in your FROM statement.
SELECT region, name, MAX(population)
FROM bbc
GROUP BY region, name