[GitHub] [spark] viirya commented on a diff in pull request #36809: [SPARK-39488][SQL] Simplify the error handling of TempResolvedColumn

[GitBox <gi...@apache.org>]

viirya commented on code in PR #36809:
URL: https://github.com/apache/spark/pull/36809#discussion_r898623736


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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala:
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@@ -4345,32 +4340,42 @@ object ApplyCharTypePadding extends Rule[LogicalPlan] {
 }
 
 /**
- * Removes all [[TempResolvedColumn]]s in the query plan. This is the last resort, in case some
- * rules in the main resolution batch miss to remove [[TempResolvedColumn]]s. We should run this
- * rule right after the main resolution batch.
+ * The rule `ResolveAggregationFunctions` in the main resolution batch creates
+ * [[TempResolvedColumn]] in filter conditions and sort expressions to hold the temporarily resolved
+ * column with `agg.child`. When filter conditions or sort expressions are resolved,
+ * `ResolveAggregationFunctions` will turn [[TempResolvedColumn]] to [[AttributeReference]] if it's
+ * inside aggregate functions or group expressions, or turn it to [[UnresolvedAttribute]] otherwise,
+ * hoping other rules can resolve it.
+ *
+ * This rule runs after the main resolution batch, and can still hit [[TempResolvedColumn]] if
+ * filter conditions or sort expressions are not resolved. When this happens, there is no point to

Review Comment:
   It reads like a contradiction here. `ResolveAggregationFunctions` will turn `TempResolvedColumn` to `UnresolvedAttribute` and hope other rules can resolve it.
   
   So why `RemoveTempResolvedColumn` can hit `TempResolvedColumn`? If it is not resolved, isn't it turned to `UnresolvedAttribute`?
   



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