[GitHub] [drill] vvysotskyi commented on a change in pull request #1839: DRILL-4517: Support reading empty Parquet files

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

vvysotskyi commented on a change in pull request #1839: DRILL-4517: Support reading empty Parquet files
URL: https://github.com/apache/drill/pull/1839#discussion_r312738641
 
 

 ##########
 File path: exec/java-exec/src/main/java/org/apache/drill/exec/expr/IsPredicate.java
 ##########
 @@ -121,15 +121,28 @@ static boolean hasNoNulls(ColumnStatistics stat) {
   }
 
   /**
-   * Checks that column chunk's statistics has only nulls
+   * Checks that column chunk's statistics has only nulls.
+   * <p/>
+   * Besides comparing number of nulls, we need to check
+   * if min and max values are also nulls to cover use cases for arrays,
+   * since array can hold N number of elements and nulls statistics
+   * is collected for all elements, thus number of nulls may be greater
+   * or equal to the number of rows.
+   * <p/>
+   * Two rows: [null, {"id": 1}], [null, {"id": 2]]
 
 Review comment:
   ```suggestion
      * Two rows: [null, {"id": 1}], [null, {"id": 2}]
   ```

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