minyyy opened a new pull request #35866:
URL: https://github.com/apache/spark/pull/35866
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### What changes were proposed in this pull request?
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This PR makes GeneratorNestedColumnAliasing only be able to apply to
GetStructField*(_: AttributeReference), here GetStructField* means nested
GetStructField. The current way to collect expressions is a top-down way and it
actually only checks 2 levels which is wrong. The rule is simple - If we see
expressions other than GetStructField, we are done. When an expression E is
pushed down into an Explode, the thing happens is:
E(x) is now pushed down to apply to E(array(x)).
So only expressions that can operate on both x and array(x) can be pushed.
GetStructField is special since we have GetArrayStructFields and when
GetStructField is pushed down, it becomes GetArrayStructFields. Any other
expressions are not applicable.
We also do not even need to check the child type is Array(Array()) or
whether the rewritten expression has the pattern
GetArrayStructFields(GetArrayStructFields()).
1. When the child input type is Array(Array()), the ExtractValues
expressions we get will always start from an innermost GetArrayStructFields, it
does not align with GetStructField*(x).
2. When we see GetArrayStructFields(GetArrayStructFields()) in the rewritten
generator, we must have seen a GetArrayStructFields in the expressions before
pushdown.
### Why are the changes needed?
It fixes some correctness issues. See the above section for more details.
### Does this PR introduce _any_ user-facing change?
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No
### How was this patch tested?
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Unit tests.
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