Add record, dimension value measure value data types

[Stiivi]

Add datatypes representing database record Record, value of dimension key and numeric value of measures/aggregates. Suggestion:

MeasureValueType = Union[int, float]

DimensionValueType = Union[int, str]
# Or if we decide to support Nulls (discouraged, but people have all sorts of data out there):
DimensionValueType = Optional[Union[int, str]]

RecordValueType = Union[MeasureValueType, DimensionValueType]
# Alternative with nulls:
RecordValueType = Optional[Union[MeasureValueType, DimensionValueType]]

RecordType = Mapping[str, RecordValueType]

Questions

• Do we allow NULLs?
• If yes, when and how?
• Is there a need to have two versions of Record type with Optional and not-Optional values?

Affected

• AggregationResult.cells and .summary
• Browser.aggregate()
• HierarchyPath
• SQL backend: browser and execution

See also

• #409 – Investigate use and effects of None path values

[Stiivi]

Updated description: changed names to *Type and added questions/comments about optionals/NULL values.