SQL queries/statements with special characters in comments (or maybe elsewhere?) will fail in a way that the query does not produce any results. This applies for characters like è, é, ä, ü, etc.
SELECT Name, Population FROM Country -- sélectionner uniquement les pays du continent donné WHERE Continent = :Continent
Please avoid special characters in SQL statement. Although this looks like it would be a simple fix, it is technically not as trivial as one might think.