[GitHub] [spark] HyukjinKwon commented on a change in pull request #27728: [SPARK-25556][SPARK-17636][SPARK-31026][SPARK-31060][SQL][test-hive1.2] Nested Column Predicate Pushdown for Parquet

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HyukjinKwon commented on a change in pull request #27728: [SPARK-25556][SPARK-17636][SPARK-31026][SPARK-31060][SQL][test-hive1.2] Nested Column Predicate Pushdown for Parquet
URL: https://github.com/apache/spark/pull/27728#discussion_r394853243
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/sources/filters.scala
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 @@ -32,6 +33,7 @@ import org.apache.spark.annotation.{Evolving, Stable}
 sealed abstract class Filter {
   /**
    * List of columns that are referenced by this filter.
+   * Note that, if a column contains `dots` in name, it will be quoted to avoid confusion.
 
 Review comment:
   https://github.com/apache/spark/pull/27728/files#r390853911, I think it shouldn't be a legacy configuration but a proper configuration might list which source will take the nested filter-push down.
   
   There is no workaround for the behaviour change except this legacy configuration; but legacy configurations are supposed to be removed. If we're going to add this as a legacy configuration, we should have a way to don't unquote this.
   
   Quoting itself might not exist in some downstream datasource implementations. Dots can be used for different meanings such as namespaces. Some source don't have nested structures at all and presumably they won't also have such quotes at all.
   
   

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