Github user rdblue commented on the pull request:
https://github.com/apache/spark/pull/12239#issuecomment-217275958
@liancheng, I originally had the logic you suggest for the expected columns
calculation. But, there were [test
failures](https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/57909/consoleFull)
because `OneRowRelation` reports its output columns as `Nil` and will never
match the input. Changing that introduced a huge number of test failures where
other code depended on that Nil, so I think the best way forward is to catch
the case where the output table has no columns and consider the node resolved.
The down side to this approach is that tables that actually have no columns
would be considered resolved, but we will catch this case in later processing.
For example, the `OneRowRelation` test is actually looking for a helpful error
message that you can't write to an RDD-based relation.
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