cashmand opened a new pull request, #39718:
URL: https://github.com/apache/spark/pull/39718
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### What changes were proposed in this pull request?
In parquet schema pruning, we use SelectedField to try to extract the field
that is used in a struct. It looks through GetArrayItem/GetMapItem, but when
doing so, it ignores the index/key, which may itself be a struct field. If it
is a struct field that is not selected in some other expression, and another
field of the same attribute is selected, then pruning will drop the field,
resulting in an optimizer error.
This change modifies SelectedField to only look through
GetArrayItem/GetMapItem if the index/key argument is foldable. The equivalent
code for `ElementAt` was already doing the same thing, so this just makes them
consistent.
In principle, we could continue to traverse through these expressions, we'd
just need to make sure that the index/key expression was also surfaced to
column pruning as an expression that needs to be examined. But this seems like
a fairly non-trivial change to the design of the SelectedField class.
There is some risk that the current approach could result in a regression
e.g. if there is an existing GetArrayItem that is being successfully pruned,
where a non-foldable index argument happens to not trigger an error (because it
is not a struct field, or it is preserved due to some other expression).
### Why are the changes needed?
Allows queries that previously would fail in the optimizer to pass.
### Does this PR introduce _any_ user-facing change?
Yes, as described above, there could be a performance regression if a query
was previously pruning through a GetArrayItem/GetMapItem, and happened to not
fail.
### How was this patch tested?
Unit test included in patch, fails without the patch and passes with it.
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