合并Pandas多索引DataFrame和单索引Pandas DataFrame

import pandas as pd

# 多索引DataFrame
df1 = pd.DataFrame({'A': [1, 2, 3], 'B': [4, 5, 6]}, index=pd.MultiIndex.from_tuples([('a', 'x'), ('b', 'y'), ('c', 'z')], names=['index1', 'index2']))
# 单索引DataFrame
df2 = pd.DataFrame({'C': [7, 8, 9]}, index=['a', 'b', 'c'])

merged_df = df1.merge(df2, left_on=df1.index.get_level_values(0), right_index=True)

print(merged_df)