ref property
Which source this is, for the columns that belong to it.
Generated columns name a MssqlSourceRef rather than a qualifier, and
this is the other half: as the query writes its FROM and its joins, it
tells the statement what each source ended up being called. A source with
no ref — a hand-written MssqlSource('dbo.Orders') — binds nothing, and
untyped columns go on writing their own qualifiers.
Implementation
final MssqlSourceRef? ref;