Github user cloud-fan commented on the pull request:
https://github.com/apache/spark/pull/9123#issuecomment-148306333
I wanna explain a bit more about this bug.
When we resolve sort ordering, we will use a [special
method](https://github.com/apache/spark/blob/master/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala#L429-L447),
which only resolves `UnresolvedAttributes` and `UnresolvedExtractValue`.
However, for something like `Floor('a)`, even the `'a` is resolved, the floor
expression may still being unresolved as data type mismatch(for example, `'a`
is string type and `Floor` need double type), thus can't pass [this
filter](https://github.com/apache/spark/blob/master/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala#L485),
and we can't push down this missing attribute `'a`.
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