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[SPARK-2509][SQL] Add optimization for Substring. #1428

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ueshin wants to merge 1 commit into from
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[SPARK-2509][SQL] Add optimization for Substring. #1428

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3 changes: 3 additions & 0 deletions sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
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Expand Up @@ -171,6 +171,9 @@ object NullPropagation extends Rule[LogicalPlan] {
case Literal(candidate, _) if candidate == v => true
case _ => false
})) => Literal(true, BooleanType)
case e @ Substring(Literal(null, _), _, _) => Literal(null, e.dataType)
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@rxin rxin Jul 16, 2014

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Is this not doable with constant folding?

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@rxin rxin Jul 16, 2014

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Now I think about it more, this is probably ok to leave it here since in constant folding we don't really special case for null literals. However, I looked into other rules in NullPropagation and a lot of them don't really belong there... (has nothing to do with your PR though)

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@ueshin ueshin Jul 16, 2014

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@rxin, thank you for your comment.
The rule ConstantFolding can be applied only if the expression is foldable, i.e. ALL of the child expressions are foldable, and the NullPropagation covers the case there exists at least one null literal regardless of foldabilities of the others.
So I think the cases are needed.

BTW, Substring can be foldable, right?

case e @ Substring(_, Literal(null, _), _) => Literal(null, e.dataType)
case e @ Substring(_, _, Literal(null, _)) => Literal(null, e.dataType)
// Put exceptional cases above if any
case e: BinaryArithmetic => e.children match {
case Literal(null, _) :: right :: Nil => Literal(null, e.dataType)
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