Database: Allow selectFieldValues() to accept SQL fragments

Database: Allow selectFieldValues() to accept SQL fragments

The documentation says "This must be a valid SQL fragment", but as
written it breaks if given anything other than a field name. It's easy
enough to fix by adding an alias to the internal select() call.

Bug: T201781
Change-Id: I76428af6d3aadc266254fdb24109a0ac2db3761f