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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