fix: skip adding another plan when no data file groups left during table scan

[gruuya]

Closes #217.

[JanKaul]

Thanks for the PR! I can have a look at the error. Looks like something with Materialized Views.

[gruuya]

Thanks for the PR! I can have a look at the error. Looks like something with Materialized Views.

Oh thanks, just force-pushed a fix before seeing your message.

It seems that sometimes there can be no plans and no data file groups either, so in that case it's useful to use the no-op plan.

[gruuya]

That said it might be a bit more elegant to not rely on the no-op/empty parquet scan and instead be more explicit with

    match plans.len() {
        0 => {
            let projected_schema = projection
                .map(|p| arrow_schema.project(&p))
                .transpose()?
                .unwrap_or(arrow_schema.as_ref().clone());
            Ok(Arc::new(EmptyExec::new(Arc::new(projected_schema))))
        }
        1 => Ok(plans.remove(0)),
        _ => Ok(Arc::new(UnionExec::new(plans))),
    }

Let me know what you think about that.

[JanKaul]

Yeah, I think that would be best. Thanks again!