Why uuid is only assigned for create_dataframe, not assigned for read_xxx #996

I find that uuid is assigned for create_dataframe, but not for read_csv.

it's confusing, when I join two dataframe.

when I join dataframes created from create_dataframe, there's no column name conflict, because two dataframes have different qualifiers.
but it's not that case for read_csv.

maybe it's better to make these methods have similar behavior.