[DF] Qualified projections fail

[jdye64]

Is your feature request related to a problem? Please describe.
When fully qualified projects are present in the project clause dask-sql errors out. Currently it seems the qualifier is being ignored. Since no qualifier is present and join queries that might have the same column name, dask-sql is unable to determine which schema to pull the reference from and throws an error.

Describe the solution you'd like
Properly handle fully qualified projections in the select clause and do not throw an exception.

Describe alternatives you've considered
None

Additional context
Example minimum reproducer query.

select d1.week
from date_dim d1
join date_dim d2

[jdye64]

#512 closed this issue.