Answers for "inner merge dataframes"

pandas left join

df.merge(df2, left_on = "doc_id", right_on = "doc_num", how = "left")

combine two dataframe in pandas

# Stack the DataFrames on top of each other
vertical_stack = pd.concat([survey_sub, survey_sub_last10], axis=0)

# Place the DataFrames side by side
horizontal_stack = pd.concat([survey_sub, survey_sub_last10], axis=1)