[jira] [Resolved] (SPARK-38059) Incorrect query ordering with flatMap() and distinct()

["Hyukjin Kwon (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-38059?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Hyukjin Kwon resolved SPARK-38059.
----------------------------------
    Resolution: Cannot Reproduce

> Incorrect query ordering with flatMap() and distinct()
> ------------------------------------------------------
>
>                 Key: SPARK-38059
>                 URL: https://issues.apache.org/jira/browse/SPARK-38059
>             Project: Spark
>          Issue Type: Bug
>          Components: Optimizer
>    Affects Versions: 3.0.2, 3.2.0
>            Reporter: AJ Bousquet
>            Priority: Major
>
> I have a Dataset of non-unique identifiers that I can use with {{Dataset::flatMap()}} to create multiple rows with sub-identifiers for each id. When I run the code below, the {{limit(2)}} call is placed _after_ the call to {{flatMap()}} in the optimized logical plan. This unexpectedly yields only 2 rows, when I would expect it to yield 6.
> {code:java}
> StructType idSchema = DataTypes.createStructType(List.of(DataTypes.createStructField("id", DataTypes.LongType, false)));
> StructType flatMapSchema = DataTypes.createStructType(List.of(
>     DataTypes.createStructField("id", DataTypes.LongType, false),
>     DataTypes.createStructField("subId", DataTypes.LongType, false)
> ));Dataset<Row> inputDataset = context.sparkSession().createDataset(
>     LongStream.range(0,5).mapToObj((id) -> RowFactory.create(id)).collect(Collectors.toList()),
>     RowEncoder.apply(idSchema)
> );
> return inputDataset
>     .distinct()
>     .limit(2)
>     .flatMap((Row row) -> {
>         Long id = row.getLong(row.fieldIndex("id"));        return LongStream.range(6,8).mapToObj((subid) -> RowFactory.create(id, subid)).iterator();
>     }, RowEncoder.apply(flatMapSchema));  {code}
> When run, the above code produces something like:
> ||id||subID||
> |0|6|
> |0|7|
> But I would expect something like:
> ||id||subID||
> |1|6|
> |1|7|
> |1|8|
> |0|6|
> |0|7|
> |0|8|



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