Make ECSql Units aware

[ColinKerr]

EC schemas contain units information but ECSql doesn't use that information.

Consider supporting the following things:

• Unit information exposed via query results metadata
• Explicit unit conversion e.g. SELECT Length @ 'Units:FT' FROM Pipe returns the value of length converted to feet.
• Unit aware math. e.g. SELECT Length + '2 Units.IN' FROM Pipe returns the length in persistence units (M) with 2 inches added. Or SELECT Length * Width FROM Door would return an area in meters squared
  • Consider other options for how to encode units in literals.
• Any operation using incompatible units should fail. e.g. if Length has no or incompatible persistence unit defined the operation will fail with a descriptive error

Support should not include:

• Numeric string formatting support, it should only return the converted double value.
• Automatic detection of presentation unit and auto conversion to it. ECSql should always include explicit input defining the presentation unit.

Existing implementation to in Postgres: https://github.com/df7cb/postgresql-unit

[glenworrall]

Thanks @ColinKerr , is there an opportunity to add a rowFormat
ECSQLRowFormat such as useImperialPropertyUnits so that units are returned as ft etc,
ie the challenge is sometimes not knowing if a property is a string or a value and as such there is a lot of querying of the schema to prep the UI
ie if iModelConsole had the ability then users would be able to query in their preferred format, much as they do with Design Review now