Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/21745#discussion_r201971954
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
---
@@ -1167,7 +1169,8 @@ class Analyzer(
case p: Project =>
val maybeResolvedExprs = exprs.map(resolveExpression(_, p))
val (newExprs, newChild) =
resolveExprsAndAddMissingAttrs(maybeResolvedExprs, p.child)
- val missingAttrs = AttributeSet(newExprs) --
AttributeSet(maybeResolvedExprs)
+ // Only add missing attributes coming from `newChild`.
+ val missingAttrs = (AttributeSet(newExprs) --
p.outputSet).intersect(newChild.outputSet)
--- End diff --
The logic gets convoluted here and we need to add comments. Basically we
need to explain when we should expand the project list.
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