[GitHub] [spark] sigmod commented on pull request #32298: [SPARK-34079][SQL] Merge non-correlated scalar subqueries

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

sigmod commented on pull request #32298:
URL: https://github.com/apache/spark/pull/32298#issuecomment-1075406139


   One high level comment. 
   
   Does it make sense to implement the rewrite in the following way?
   
   ```
   SELECT
     (SELECT avg(a) FROM t GROUP BY b),
     (SELECT sum(b) FROM t GROUP BY b)
   FROM T
   ```
   
   =>
   ```
   WITH cte AS (SELECT avg(a) a, sum(b) b FROM t GROUP BY b)
   SELECT (SELECT a FROM cte), (SELECT b FROM cte)
   FROM T
   ```
   
   Since we already have [WithCTE](https://github.com/apache/spark/blob/efe43306fcab18f076f755c81c0406ebc1a5fee9/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/basicLogicalOperators.scala#L703-L710) and [CTERelationRef](https://github.com/apache/spark/blob/efe43306fcab18f076f755c81c0406ebc1a5fee9/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/basicLogicalOperators.scala#L678-L686), the rewrite looks similar to what you want to achieve, while do not need to add yet-another Logical/Exec node? 


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