[FlightRPC] Flight SQL: Clarify semantics of GetSchema when binding parameters

[lidavidm]

Describe the enhancement requested

Currently it appears there are two redundant ways to get the schema of the result set of a prepared statement: either by reading the dataset_schema from the result of CreatePreparedStatement, or by making a separate GetSchema call. However, the two are not equivalent when bind parameters exist; binding a parameter may change the schema of the result set. We should clarify the purpose of these calls in Flight SQL as a result.

Experimentally, the PostgreSQL JDBC driver handles this: if you look at the MetaData before and after binding parameters, the column types will be updated to reflect your parameters.

Component(s)

FlightRPC