[GitHub] [spark] francis0407 opened a new pull request #24321: SPARK-27411: DataSourceV2Strategy should not eliminate subquery

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francis0407 opened a new pull request #24321: SPARK-27411: DataSourceV2Strategy should not eliminate subquery 
URL: https://github.com/apache/spark/pull/24321
 
 
   ## What changes were proposed in this pull request?
   
   In DataSourceV2Strategy, it seems we eliminate the subqueries by mistake after normalizing filters.
   We have an sql with a scalar subquery:
   
   ``` scala
   val plan = spark.sql("select * from t2 where t2a > (select max(t1a) from t1)")
   plan.explain(true)
   ```
   
   And we get the log info of DataSourceV2Strategy:
   ```
   Pushing operators to csv:examples/src/main/resources/t2.txt
   Pushed Filters: 
   Post-Scan Filters: isnotnull(t2a#30)
   Output: t2a#30, t2b#31
   ```
   
   The `Post-Scan Filters` should contain the scalar subquery, but we eliminate it by mistake.
   ```
   == Parsed Logical Plan ==
   'Project [*]
   +- 'Filter ('t2a > scalar-subquery#56 [])
      :  +- 'Project [unresolvedalias('max('t1a), None)]
      :     +- 'UnresolvedRelation `t1`
      +- 'UnresolvedRelation `t2`
   
   == Analyzed Logical Plan ==
   t2a: string, t2b: string
   Project [t2a#30, t2b#31]
   +- Filter (t2a#30 > scalar-subquery#56 [])
      :  +- Aggregate [max(t1a#13) AS max(t1a)#63]
      :     +- SubqueryAlias `t1`
      :        +- RelationV2[t1a#13, t1b#14] csv:examples/src/main/resources/t1.txt
      +- SubqueryAlias `t2`
         +- RelationV2[t2a#30, t2b#31] csv:examples/src/main/resources/t2.txt
   
   == Optimized Logical Plan ==
   Filter (isnotnull(t2a#30) && (t2a#30 > scalar-subquery#56 []))
   :  +- Aggregate [max(t1a#13) AS max(t1a)#63]
   :     +- Project [t1a#13]
   :        +- RelationV2[t1a#13, t1b#14] csv:examples/src/main/resources/t1.txt
   +- RelationV2[t2a#30, t2b#31] csv:examples/src/main/resources/t2.txt
   
   == Physical Plan ==
   *(1) Project [t2a#30, t2b#31]
   +- *(1) Filter isnotnull(t2a#30)
      +- *(1) BatchScan[t2a#30, t2b#31] class org.apache.spark.sql.execution.datasources.v2.csv.CSVScan
   ```
   ## How was this patch tested?
   
   ut
   

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