um FULL JOIN
zu simulieren in mysql müssen Sie UNION
das Ergebnis von Right Join und Left Join aus beiden Tabellen
SELECT Persons.Name, Persons.P_Id, Invoice.Id
FROM Persons
LEFT JOIN Invoice
ON Persons.P_Id=Invoice.P_Id
UNION
SELECT Persons.Name, Persons.P_Id, Invoice.Id
FROM Invoice
LEFT JOIN Persons
ON Persons.P_Id=Invoice.P_Id