[GitHub] [spark] wangyum commented on pull request #30222: [SPARK-33315][SQL] Simplify CaseWhen with EqualTo

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wangyum commented on pull request #30222:
URL: https://github.com/apache/spark/pull/30222#issuecomment-722858604


   We can reproduce it by:
   ```scala
   spark.sql("CREATE TABLE t(a int, b int, c int) using parquet")
   spark.sql(
     """
       |SELECT *
       |  FROM   (SELECT CASE
       |    WHEN rd > 1 THEN 1
       |    WHEN b > 1000 THEN 2
       |    WHEN c < 100 THEN 3
       |    ELSE 4
       |END AS x
       |FROM (SELECT *, rand(100) as rd FROM t) t1) t2
       |WHERE  x = 2
       |""".stripMargin).explain
   ```
   
   1. `Alias.toAttribute` construct `AttributeReference` with default 
deterministic, that is true:
   
https://github.com/apache/spark/blob/ca2cfd4185586993f981cfd2f1aff30ee6b2294e/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/namedExpressions.scala#L181
   
   2. Therefore, deterministic is true, and`SimplifyConditionals` can simplify 
it:
   
![image](https://user-images.githubusercontent.com/5399861/98330987-9aa8ab00-2036-11eb-8acf-93f1a2b9f404.png)
   


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