Add `CAST` to `parser.py`

[jayceslesar]

Feature Request / Improvement

I think I have somewhat of an idea on how to do this, so far have added the following to parser.py:

CAST = CaselessKeyword("cast")
cast_expression = (CAST + "(" + column + "as" + identifier + Suppress(")")).set_results_name("cast")

# would need something special for the set_parse_action

I am wondering a couple of things:
Do we need a new class CastableReference or something? Worth expanding on the Reference class? And once that is done, how would we propagate the new type (Im assuming we need some way to go from a string to an IcebergType of the string the user has put into the cast operation) into the scan?

This was spawned from #170

Happy to work on this, just would be awesome to get some context

[Fokko]

Hey @jayceslesar Thanks for splitting out this task!

For inspiration on how to name things, we try to keep in line with the Java library where possible. This makes it easier for folks to switch between the projects. In Java this would result in a UnboundTransform. Unbound meaning that we don't know the type of the column yet.

CAST(created_at AS date) -> UnboundTransform(Reference("created_at"), DayTransform())

Once we know the type, we can bind the transform and see if it is a valid cast. Does this help?

[jayceslesar]

hey @Fokko, ive been playing around with it and am wondering if the BoundTransform needs to be updated to take in a Reference like it does in the java version? Been a couple years since I have written java

[Fokko]

@jayceslesar No we need to add the UnboundTransform in Python 👍

[jayceslesar]

@Fokko I think im close -- will have a draft MR shortly

[github-actions]

This issue has been automatically marked as stale because it has been open for 180 days with no activity. It will be closed in next 14 days if no further activity occurs. To permanently prevent this issue from being considered stale, add the label 'not-stale', but commenting on the issue is preferred when possible.

[github-actions]

This issue has been closed because it has not received any activity in the last 14 days since being marked as 'stale'