from typing import Tuple


def create_columns(column_def: Tuple[str, str]) -> str:
    """
    Prepare columns for table create as follows:
    - types copied from target table
    - no indexes or constraints (no serial, no unique, no primary key etc.)
    """
    return (','.join(f'{k} {v}' for k, v in column_def)
        .replace('bigserial', 'bigint')
        .replace('smallserial', 'smallint')
        .replace('serial', 'integer')
    )