def insert_clause(table_name, keys):
    """ Create a insert clause string for SQL.

        Args:
            table_name: The table where the insertion will happen.
            keys: An iterator with strings specifying the fields to change.
        
        Returns:
            The query as a string
    """
    fields = list(keys)

    fields_str = ', '.join(fields)
    values_str = ', '.join(['?']*len(fields))

    query = 'INSERT INTO {} ({}) VALUES ({})'.format(table_name, fields_str, values_str)
    return query