we can call sqlglot_types.from_bigframes_dtype instead and remove "# type: igore"

Yeah better.

to="INT64" works too and can simple the expression a little bit. If so, can we apply to all the "to" parameter of the "sge.Cast" method?

Yeah it works.

Style nit: could we define separate helper functions to handle different frequencies? This would help reduce the size of the function _integer_label_to_datetime_op_non_fixed_frequency and improve readability.

The improved function should look like this

def _integer_label_to_datetime_op_non_fixed_frequency():
    ....
    if rule_code is weekly:
        return _integer_label_to_datetime_op_weekly_freq()
    elif rule_code is monthly:
         ....

Done.

For better readability, can we move this "if" clauses to the integer_label_to_datetime_op function"? In this way, we don't need to raise "ValueError" anymore. The expected function integer_label_to_datetime_op would be like:

    if rule_code == "W-SUN":
        return _integer_label_to_datetime_op_weekly_freq(x, y, op)
....

   # Instead raise ValueError, we can call function directly.
   return _integer_label_to_datetime_op_non_fixed_frequency(x, y, op)

I’ve flattened the logic as suggested, but kept the ValueError to explicitly handle cases with an unsupported frequency rule code (e.g. rule_code='an_unsupported_value') so that this implementation’s error-handling remains consistent with the original logic: e.g. when both rule_code and op.freq.nanos have valid values, it should go to the non-fixed frequency case, not the fixed one.

Thanks for looking into it. It sounds reasonable to me.