[GitHub] [spark] cloud-fan commented on pull request #35248: [SPARK-37960][SQL] Support aggregate push down with `CASE ... WHEN ... ELSE ... END`

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cloud-fan commented on pull request #35248:
URL: https://github.com/apache/spark/pull/35248#issuecomment-1032681495


   @beliefer Please enrich the PR description to explain the motivation of this approach. It's a new framework to represent catalyst expressions in DS v2 APIs, and CASE WHEN is just the first use case.
   
   To @HyukjinKwon , I proposed this idea because it's too much work to duplicate all the catalyst expressions in DS v2 with Java classes. In fact, the current basic DS v2 predicate/aggregate expressions should be sufficient for simple data sources that are file-based. It turns out that the sources which need advanced pushdown support are almost all SQL systems like Oracle, Clickhouse, etc., and it's actually better for them to get a SQL string directly, instead of building SQL string manually from DS v2 expressions.


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