cloud-fan commented on code in PR #46143:
URL: https://github.com/apache/spark/pull/46143#discussion_r2828758300
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/AliasHelper.scala:
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@@ -65,6 +65,30 @@ trait AliasHelper {
})
}
+ /**
+ * Replace all attributes, that reference an alias, with the aliased
expression.
+ * Tracks which aliases were replaced and returns them.
+ */
+ protected def replaceAliasWhileTracking(
+ expr: Expression,
+ aliasMap: AttributeMap[Alias]): (Expression, AttributeMap[Alias]) = {
+ // Use transformUp to prevent infinite recursion when the replacement
expression
+ // redefines the same ExprId,
+ var replaced = AttributeMap.empty[Alias]
+ val newExpr = trimAliases(expr.transformUp {
+ case a: Attribute =>
+ // If we replace an alias add it to replaced
+ val newElem = aliasMap.get(a)
+ newElem match {
+ case None => a
+ case Some(b) =>
+ replaced += (a, b)
Review Comment:
we should skip this operation if the AttributeMap already contains `a`. It
does not change the result but is more efficient.
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