[GitHub] [spark] HyukjinKwon commented on pull request #30984: [SPARK-33915][SQL] Allow json expression to be pushable column

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

HyukjinKwon commented on pull request #30984:
URL: https://github.com/apache/spark/pull/30984#issuecomment-757409794


   @tedyu, the special characters are not allowed in some sources such as Hive as you tested. However, they are allowed in some other sources when you use DSLs:
   
   ```scala
   scala> spark.range(1).toDF("GetJsonObject(phone#37,$.phone)").write.option("header", true).mode("overwrite").csv("/tmp/foo")
   
   scala> spark.read.option("header", true).csv("/tmp/foo").show()
   +-------------------------------+
   |GetJsonObject(phone#37,$.phone)|
   +-------------------------------+
   |                              0|
   +-------------------------------+
   ```
   
   In this case, the filters will still be pushed down to the datasource implementation site. We should have a way to identify if the pushed `GetJsonObject(phone#37,$.phone)` is a field or expression pushed down.
   
   This makes me believe the current implementation based on strings are flaky, and incomplete. 


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