The hard part with making the `ErrNotSupported` message clearer is that it's no longer returned by pq. It used to be returned when `LastInsertId()` was called but as of cd527896ec38b37883721b9b26f36f3554f6cfe0 that method now uses `database/sql/driver.RowsAffected` which [returns a normal error](http://golang.org/src/pkg/database/sql/driver/driver.go?s=6050:6073#L174).

This means that any legacy code that's explicitly checking against the error string is already broken. On the other hand `LastInsertId()` was never supported by pq so I can't see how calling it then checking for a pq error class would have ever made any sense.

I'm not arguing for removing the exported variable here I think the best course of action here is probably to use the grouped os style var declaration as you suggest and change the message for ErrNotSupported to "Unsupported Command" so it's available for future use.