[GitHub] [parquet-mr] wgtmac commented on pull request #1028: PARQUET-2244: Fix notIn for columns with null values

["wgtmac (via GitHub)" <gi...@apache.org>]

wgtmac commented on PR #1028:
URL: https://github.com/apache/parquet-mr/pull/1028#issuecomment-1432527608

   > I did a quick test using Spark
   > 
   > ```
   >           Seq("A", "A", null).toDF("column").repartition(1).write.mode("overwrite").parquet("t")
   >           spark.read.parquet("t").where("NOT (column <=> 'A')").show    // this returns null
   >           spark.read.parquet("t").where("NOT (column = 'A')").show    // this returns empty
   >           spark.read.parquet("t").where("column IN ('A')").show    // this returns A A
   >           spark.read.parquet("t").where("column NOT IN ('A')").show    // this returns empty
   > ```
   > 
   > If we only has `A` and `null` for `column` and we have predicate `column not in ('A')`, should we return empty instead of null?
   
   IIUC, 
   - `col IN (A, B)` is equal to `col = A OR col = B`
   - `col NOT IN (A, B)` is equal to `col <> A AND col <> B`. where `col <> A` means `col IS NOT NULL and col != A`
   
   So my answer to your question above is empty. @huaxingao 
   
   It seems that we lose the chance to skip the row group with this fix. @gszadovszky 


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