pandas.merge(df1, df2, how='left', left_on=['id_key'], right_on=['fk_key'])
Here is what the above code is Doing:
1. We’re merging df1 and df2 on the left.
2. We’re merging on the id_key column of df1 and the fk_key column of df2.
3. We’re using a left join, which means all rows in df1 will be kept, and if there are missing values of the fk_key in df2,
those will be filled with NaN values.