Checking multi-table joins
Have a look at the results for Albania from the previous query below. You can see that the 2015 fertility_rate has been paired with 2010 unemployment_rate, and vice versa.
| name | year | fertility_rate | unemployment_rate |
|---|---|---|---|
| Albania | 2015 | 1.663 | 17.1 |
| Albania | 2010 | 1.663 | 14 |
| Albania | 2015 | 1.793 | 17.1 |
| Albania | 2010 | 1.793 | 14 |
Instead of four records, the query should return two: one for each year. The last join was performed on c.code = e.code, without also joining on year. Your task in this exercise is to fix your query by explicitly stating that both the country code and year should match!
This exercise is part of the course
Joining Data in SQL
Exercise instructions
- Modify your query so that you are joining to
economiesonyearas well ascode.
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
SELECT name, e.year, fertility_rate, unemployment_rate
FROM countries AS c
INNER JOIN populations AS p
ON c.code = p.country_code
INNER JOIN economies AS e
ON c.code = e.code
-- Add an additional joining condition such that you are also joining on year
___;