SELECT .. SELECT

The Derived Table (SELECT FROM SELECT)

List the largest country for each region

Sometimes you need to use the results from one query in another. To show the largest country (by population) for each region you can join the list of countries to the list of regions (with max populations).

For example you can get the maximum population for each region using:

 SELECT region, MAX(population) AS maxpop
  FROM bbc
 GROUP BY region

Note that this gives the population of the largest country - it does not give you the name of that country.

region	maxpop
Africa	130200000
Americas	13000000
Asia-Pacific	1300000000
Europe	141500000
Middle East	74900000
North America	295000000
South America	182800000
South Asia	1100000000

You may use a SELECT statement in the FROM line. In this example the table is beast and the columns are id and legs.

SELECT name, A.region
  FROM bbc AS A JOIN
  (SELECT region,MAX(population) AS maxpop
     FROM bbc
   GROUP BY region) AS B
  ON (A.region=B.region 
  AND A.population=maxpop)

SELECT name, A.region
 FROM bbc AS A JOIN
 (SELECT region,MAX(population) AS maxpop
    FROM bbc
  GROUP BY region) AS B
 ON (A.region=B.region AND A.population=maxpop)

What about ties?

If one region has two countries with the same, highest population then the query will produce the right answers but there will be duplication- both countries will be shown.

See also:

• SELECT in SELECT Tutorial
• SELECT JOIN