Allow function results in group by

Allow grouping by function result. This is especially useful with datetime fields. A simple example from postgresql :

SELECT EXTRACT(YEAR from date_column) FROM sales group by EXTRACT(YEAR from date_column)

You can see how this is useful when creating for example yearly, monthly or daily sales results. Without this functionality you need to denormalize your table so year , month and day stays in separate columns.

[long2ice]

OK, this should be a new feature

[MrAngry]

I could also add code for ProductModel and District but I think it is not important as those fields do not play any role here. And trying to use annotation does not work as well:

sales= Sales.all()
sales = await sales.annotate(year=Extract(F('date'), 'YEAR')).group_by('year').values('year')

tortoise.exceptions.FieldError: Unknown field "year" for model "Sales"