[GitHub] [spark] wangyum edited a comment on pull request #31739: [SPARK-34622][SQL] Push down limit through Project with Join

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wangyum edited a comment on pull request #31739:
URL: https://github.com/apache/spark/pull/31739#issuecomment-805359628


   > Last question: do we push down limit through project?
   
   It seems push down limit through project no benefit:
   ```scala
   spark.range(2000L).selectExpr("id AS a", "id AS b").write.saveAsTable("t1")
   spark.sql("select a, java_method('java.lang.Thread', 'sleep', 3000L) from t1 limit 5").show()
   spark.sql("select a, java_method('java.lang.Thread', 'sleep', 3000L) from (select * from t1 limit 5) t limit 5").show()
   ```
   
   ```
   == Optimized Logical Plan ==
   GlobalLimit 5
   +- LocalLimit 5
      +- Project [a#16L, java_method(java.lang.Thread, sleep, 3000) AS java_method(java.lang.Thread, sleep, 3000)#18]
         +- Relation default.t1[a#16L,b#17L] parquet
   ```
   
   ```
   == Optimized Logical Plan ==
   Project [a#16L, java_method(java.lang.Thread, sleep, 3000) AS java_method(java.lang.Thread, sleep, 3000)#21]
   +- GlobalLimit 5
      +- LocalLimit 5
         +- Project [a#16L]
            +- Relation default.t1[a#16L,b#17L] parquet
   ```


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