Question

SELECT c.code, c.name, c.region, p.year, p.fertility_rate, e.year, e.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; What is wrong with this query?

Answer 1

The query has an issue with ambiguous column names for 'year' from the populations and economies tables, and may need an additional join condition to match the data based on the same year if that is required.

Step-by-step explanation:

The query provided appears to join three tables: countries, populations, and economies. However, there's a potential issue with selecting columns that have the same name from two different tables without using aliases. In this case, both p.year and e.year are selected. This can create confusion or result in an error because it's unclear which year the query should refer to when presenting the data. Moreover, if the intent is to match the data from populations and economies based on the same year, there needs to be a condition specifying that the years from these two tables should be the same. To correct the wrong aspects of the query, we need to add an alias for at least one of the years' columns and possibly include a join condition that ensures the data corresponds to the same year if that is the desired outcome.