Make ScanStruct both backward and forward compatible

[recht]

I have a query like select * from table, and I use ScanStruct to map the results to a struct. Now I want to add a new column to the table, so I alter table add column, but that then breaks the query because ScanStruct fails with missing destination name "newcolumn" in *struct.

A nicer behavior would be to not fail but just ignore columns that can't be mapped, just like with unmarshalling json. That would make it much easier to roll out changes to tables as it requires less coordination.

[recht]

It's actually even worse, because when using PrepareBatch/AppendStruct to insert, the struct must also match the exact table structure, so there's basically no way to roll out a migration without breaking something, at least not when using the struct functions.