SELECT *
FROM planets
LEFT JOIN moons USING (Diameter_km)
UNION ALL
SELECT *
FROM planets
RIGHT JOIN moons USING (Diameter_Km)
ORDER BY Diameter_km;
The LEFT JOIN/UNION ALL/RIGHT JOIN was the workaround to do a FULL OUTER JOIN
Because both Tables had the “Diameter_km” Field I was able to use the USING Keyword to make the JOIN less complicated