将两个数据帧连接在一起的问题

import pandas as pd

data1 = {'key': ['A', 'B', 'C', 'D'],
         'value': [1, 2, 3, 4]}
data2 = {'key': ['B', 'D', 'E', 'F'],
         'value': [5, 6, 7, 8]}

df1 = pd.DataFrame(data1)
df2 = pd.DataFrame(data2)

merged_df = pd.merge(df1, df2, on='key', suffixes=('_left', '_right'))

  key  value_left  value_right
0   B           2            5
1   D           4            6

merged_df_all = pd.merge(df1, df2, on='key', how='outer')

  key  value_left  value_right
0   A           1          NaN
1   B           2            5
2   C           3          NaN
3   D           4            6
4   E          NaN          7
5   F          NaN          8

merged_df_multi = pd.merge(df1, df2, on=['key', 'value'], how='inner')