[jira] [Created] (SPARK-28477) Rewrite `CASE WHEN cond THEN ifTrue OTHERWISE ifFalse` END into `IF(cond, ifTrue, ifFalse`

["Josh Rosen (JIRA)" <ji...@apache.org>]

Josh Rosen created SPARK-28477:
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             Summary: Rewrite `CASE WHEN cond THEN ifTrue OTHERWISE ifFalse` END into `IF(cond, ifTrue, ifFalse`
                 Key: SPARK-28477
                 URL: https://issues.apache.org/jira/browse/SPARK-28477
             Project: Spark
          Issue Type: Improvement
          Components: Optimizer, SQL
    Affects Versions: 3.0.0
            Reporter: Josh Rosen


Spark SQL has both {{CASE WHEN}} and {{IF}} expressions.

I've seen many cases where end-users write
{code:java}
when(x, ifTrue).otherwise(ifFalse){code}
because Spark doesn't have a {{org.apache.spark.sql.functions._}} method for the {{If}} expression.

Unfortunately, {{CASE WHEN}} generates substantial code bloat because its codgen is implemented using a {{do-while}} loop. In some performance-critical frameworks, I've modified our code to directly construct the Catalyst {{If}} expression, but this is toilsome and confusing to end-users.

If we have a {{CASE WHEN}} which has only two branches, like the example given above, then Spark should automatically rewrite it into a simple {{IF}} expression.



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