What are the names of the hosts that held parties with more than 20 hosts?
SELECT T2.Name FROM party_host AS T1 JOIN HOST AS T2 ON T1.Host_ID   =   T2.Host_ID JOIN party AS T3 ON T1.Party_ID   =   T3.Party_ID WHERE T3.Number_of_hosts  >  20
names of the hosts = T2.Name; held parties with more than 20 hosts = WHERE T3.Number_of_hosts  >  20;