# df1 as main df and use the feild from df2 and map it into df1
df1.merge(df2,on='columnName',how='left')
df_outer = pd.merge(df1, df2, on='id', how='outer')
df_inner = pd.merge(df1, df2, on='id', how='inner')
>>> df.join(other.set_index('key'), on='key')
key A B
0 K0 A0 B0
1 K1 A1 B1
2 K2 A2 B2
3 K3 A3 NaN
4 K4 A4 NaN
5 K5 A5 NaN
#https://pandas.pydata.org/docs/user_guide/merging.html