Task: Text to Code
Input (English): Step 1: For each row in party table, find the corresponding rows in party_host table.
Step 2: find the number of rows of each value of party_host's Party_ID in the results of step 1.
Step 3: find Party_Theme in the results of step 1 whose corresponding value in step 2 is greater than 20
Output (English): SELECT T1.Party_Theme FROM party AS T1 JOIN party_host AS T2 ON T1.Party_ID = T2.Party_ID GROUP BY T2.Party_ID HAVING Count ( * ) > 20