ประเทศที่มีทั้งผู้เล่นตำแหน่งกองหน้าและผู้เล่นตำแหน่งกองหลังชื่ออะไร?
What are the names of countries that have both players with position forward and players with position defender?
country = pd.DataFrame(columns=['Country_name', 'Country_id']); match_season = pd.DataFrame(columns=['Country', 'Position'])
pd.merge(country, match_season[match_season['Position']=='Forward'], left_on='Country_id', right_on='Country').merge(match_season[match_season['Position']=='Defender'], left_on='Country_id', right_on='Country')['Country_name']