Github user mgaido91 commented on a diff in the pull request:
https://github.com/apache/spark/pull/19901#discussion_r155183563
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/conditionalExpressions.scala
---
@@ -180,13 +180,15 @@ case class CaseWhen(
}
override def doGenCode(ctx: CodegenContext, ev: ExprCode): ExprCode = {
- // This variable represents whether the first successful condition is
met or not.
- // It is initialized to `false` and it is set to `true` when the first
condition which
- // evaluates to `true` is met and therefore is not needed to go on
anymore on the computation
- // of the following conditions.
- val conditionMet = ctx.freshName("caseWhenConditionMet")
- ctx.addMutableState(ctx.JAVA_BOOLEAN, ev.isNull)
- ctx.addMutableState(ctx.javaType(dataType), ev.value)
+ // This variable represents whether the evaluated result is null or
not. It's a byte value
+ // instead of boolean because it carries an extra information about if
the case-when condition
+ // is met or not. It is initialized to `-1`, which means the condition
is not met yet and the
+ // result is unknown. When the first condition is met, it is set to
`1` if result is null, or
+ // `0` if result is not null. We won't go on anymore on the
computation if it's set to `1` or
+ // `0`.
+ val resultIsNull = ctx.freshName("caseWhenResultIsNull")
--- End diff --
I think there is no need to change the type of this. We can achieve the
reduction of number of variables used as you did for coalesce, thus maintaining
consistency with the rest of the code
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