a.index`` in the schema.
    primary_key : bool or None, default True
        Column names to designate as the primary key.
        The default `None` will set `'primaryKey'` to the index
        level or levels if the index is unique.
    version : bool, default True
        Whether to include a field `pandas_version` with the version
        of pandas that last revised the table schema. This version
        can be different from the installed pandas version.

    Returns
    -------
    dict

    Notes
    -----
    See `Table Schema
    <https://pandas.pydata.org/docs/user_guide/io.html#table-schema>`__ for
    conversion types.
    Timedeltas as converted to ISO8601 duration format with
    9 decimal places after the seconds field for nanosecond precision.

    Categoricals are converted to the `any` dtype, and use the `enum` field
    constraint to list the allowed values. The `ordered` attribute is included
    in an `ordered` field.

    Examples
    --------
    >>> from pandas.io.json._table_schema import build_table_schema
    >>> df = pd.DataFrame(
    ...     {'A': [1, 2, 3],
    ...      'B': ['a', 'b', 'c'],
    ...      'C': pd.date_range('2016-01-01', freq='d', periods=3),
    ...     }, index=pd.Index(range(3), name='idx'))
    >>> build_table_schema(df)
    {'fields': [{'name': 'idx', 'type': 'integer'}, {'name': 'A', 'type': 'integer'}, {'name': 'B', 'type': 'string'}, {'name': 'C', 'type': 'datetime'}], 'primaryKey': ['idx'], 'pandas_version': '1.4.0'}
    Tr*