[GitHub] [spark] huaxingao commented on pull request #29695: [SPARK-32833][SQL] [WIP]JDBC V2 Datasource aggregate push down

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huaxingao commented on pull request #29695:
URL: https://github.com/apache/spark/pull/29695#issuecomment-701722985


   @maropu Thank you very much for your review. 
   
   > Can we support aggregate pushdown with all the data types? For example, aggregating decimal values seems to have different behaviours between database implementations.
   
   Sorry I am not familiar with this. Could you please give me an example of the different implementations?
   
   > How does Spark receive aggregated values on database sides? It seems the data types of input/aggregated values are different in some databases, e.g., sum(bigint)=>numeric in PostgreSQL.
   
   I will cast the output of aggregates to the type that spark expects.
   For example, spark expects bigInt from sum(int), so the output of sum(int) from database needs to be casted to bigint.
   
   
   > How does Spark handle overflows on database sides?
   
   Not sure how to handle this yet. I will try to figure out. Please let me know if you have a good idea. 
   
   


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