country_code is defined as NOT NULL
Without a country_code for 'Marc' the second step will fail (cannot relate country_code in REL_persons to country_code in REL_countries if the REL_persons record has no value for country_code).
Since this is the whole point of this example it's going to trip people up who're trying to set up relations in phpMyAdmin (like me!)
Co-authored-by: William Desportes <williamdes@wdes.fr>
Signed-off-by: John Kershaw <john@kershaw.org>
Signed-off-by: William Desportes <williamdes@wdes.fr>