Filtering in the join, where, and select
Looking at all the countries with gross domestic product (GDP) data in 2014, the average GDP per capita was $19,342. For African countries, the average GDP per capita was $5,879.
Perhaps the African countries that sent athletes to the Olympics (Morocco, Togo, Zimbabwe) did not have the highest GDPs per capita in Africa but had higher GDPs than the average African GDP.
Test this theory. Find the per capita GDP for the African countries with athletes at the 2014 Winter Games.
This exercise is part of the course
Improving Query Performance in PostgreSQL
Exercise instructions
- The athletes' data is already limited to African competitors. Find the unique athletes from the
athletes_winttable. - Use the
JOINto filter the athletes to only those withodemographic(GDP) data. - Use a
yearfilter from theathletes_winttable to restrict results to only the 2014 athletes.
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
SELECT ___ ath.name, dem.country, dem.gdp
FROM athletes_wint ath
___ ___ odemographics dem
ON ath.country_code = dem.olympic_cc
___ ___ = ___
ORDER BY dem.gdp DESC;