SELECT .. SELECT
From SQLZOO
The Derived Table (SELECT FROM SELECT)
You can use the results from one query in another query
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, gdp_pre_capita FROM (SELECT name, gdp/population AS gdp_per_capita FROM bbc) X
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: