Logical expression ScalarVariable cannot represent an extension type or metadata #18230
Description
Is your feature request related to a problem or challenge?
The ScalarVariable is represented in terms of DataType, and thus plans can't
datafusion/datafusion/expr/src/expr.rs
Lines 313 to 314 in 6ecf76c
While we are here, it would probably be a good idea to allow the nullability to be represented here as well as most other logical expression members can store this, too.
Describe the solution you'd like
Perhaps the DataType could be updated to a FieldRef or FieldMetdata could be added
Describe alternatives you've considered
No response
Additional context
- Issue for updating Cast: LogicalPlan Casts can't express a cast to an extension type #18060
- Issue for updating Placeholder: Logical plan placeholders can't contain metadata #17862