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[SPARK-33798][SQL] Add new rule to push down the foldable expressions through CaseWhen/If #30790

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[SPARK-33798][SQL] Add new rule to push down the foldable expressions through CaseWhen/If #30790

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19b0a83
Simplify EqualTo(CaseWhen/If, Literal) always false
wangyum Dec 16, 2020
831bf66
Address comments
wangyum Dec 16, 2020
859893d
Null value should be handled by NullPropagation.
wangyum Dec 16, 2020
db584ef
Handle Null values
wangyum Dec 16, 2020
55f4528
address comments
wangyum Dec 16, 2020
0a48048
address comments
wangyum Dec 17, 2020
f9f622f
Push down EqualTo through CaseWhen/If
wangyum Dec 17, 2020
21ef0c3
Push down EqualTo through CaseWhen/If
wangyum Dec 17, 2020
d5135ec
Fix
wangyum Dec 17, 2020
8ccc3c1
fix
wangyum Dec 17, 2020
45b56fc
fix
wangyum Dec 18, 2020
cfac0e8
fix
wangyum Dec 18, 2020
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13 changes: 13 additions & 0 deletions sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -470,6 +470,11 @@ object SimplifyConditionals extends Rule[LogicalPlan] with PredicateHelper {
case _ => false
}

private def isAlwaysFalse(exps: Seq[Expression], equalTo: Literal): Boolean = {
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@dongjoon-hyun dongjoon-hyun Dec 16, 2020

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isAlwaysFalse seems to be mismatched a little with the behavior of this function. Technically, this function resembles contains function where expr is a list and equalTo literal is the item to be check the containment.

scala> Seq(1, 2).contains(3)
res0: Boolean = false

scala> Seq(1, 2).contains(2)
res1: Boolean = true

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@wangyum wangyum Dec 17, 2020

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Yes, do you have a recommended function name?

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@dongjoon-hyun dongjoon-hyun Dec 17, 2020

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Maybe, something like notEqualForAll instead of isAlwaysFalse?

exps.forall(_.isInstanceOf[Literal]) &&
exps.forall(!EqualTo(_, equalTo).eval(EmptyRow).asInstanceOf[Boolean])
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@cloud-fan cloud-fan Dec 16, 2020 •
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EqualTo may return null, we need to take care of it, because null is not false in SQL.

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@wangyum wangyum Dec 16, 2020

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Yes. Null value should be handled by NullPropagation.

}

def apply(plan: LogicalPlan): LogicalPlan = plan transform {
case q: LogicalPlan => q transformExpressionsUp {
case If(TrueLiteral, trueValue, _) => trueValue
Expand Down Expand Up @@ -523,6 +528,14 @@ object SimplifyConditionals extends Rule[LogicalPlan] with PredicateHelper {
} else {
e.copy(branches = branches.take(i).map(branch => (branch._1, elseValue)))
}

case EqualTo(i @ If(_, trueValue, falseValue), right: Literal)
if i.deterministic && isAlwaysFalse(trueValue :: falseValue :: Nil, right) =>
FalseLiteral

case EqualTo(c @ CaseWhen(branches, elseValue), right: Literal)
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@cloud-fan cloud-fan Dec 17, 2020

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A more general idea is to push down EqualTo(or other binary expressions) through If/CaseWhen.

For the example case, (CASE WHEN id = 1 THEN 'b' WHEN id = 3 THEN 'c' END) = 'a', we go through the following steps

  1. CASE WHEN id = 1 THEN 'b' = 'a' WHEN id = 3 THEN 'c' = 'a' END
  2. CASE WHEN id = 1 THEN false WHEN id = 3 THEN false END
  3. false

Step 3 may need more work in SimplifyConditionals to make it possible.

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@wangyum wangyum Dec 17, 2020

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+1 for this more general idea.

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@cloud-fan cloud-fan Dec 17, 2020

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We can create a new rule to do it, e.g. PushFoldableIntoBranches

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@wangyum wangyum Dec 17, 2020

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OK.

if c.deterministic && isAlwaysFalse(branches.map(_._2) ++ elseValue, right) =>
FalseLiteral
}
}
}
Expand Down
94 changes: 94 additions & 0 deletions ...yst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/SimplifyConditionalSuite.scala
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Expand Up @@ -199,4 +199,98 @@ class SimplifyConditionalSuite extends PlanTest with ExpressionEvalHelper with P
If(Factorial(5) > 100L, b, nullLiteral).eval(EmptyRow))
}
}

test("SPARK-33798: simplify EqualTo(If, Literal) always false") {
val a = EqualTo(UnresolvedAttribute("a"), Literal(100))
val ifExp = If(a === Literal(1), Literal(2), Literal(3))
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@cloud-fan cloud-fan Dec 16, 2020

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Let's make sure the test expression is valid. a is an EqualTo, comparing boolean and Literal(1) is invalid.


assertEquivalent(EqualTo(ifExp, Literal(4)), FalseLiteral)
assertEquivalent(EqualTo(ifExp, Literal(3)), EqualTo(ifExp, Literal(3)))
assertEquivalent(EqualTo(ifExp, Literal("4")), FalseLiteral)
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@cloud-fan cloud-fan Dec 16, 2020

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ditto, let's don't test invalid expressions, ifExp.dataType is int, not string.

assertEquivalent(EqualTo(ifExp, Literal("3")), EqualTo(ifExp, Literal(3)))

// Do not simplify if it contains non foldable expressions.
assertEquivalent(EqualTo(ifExp, NonFoldableLiteral(true)),
EqualTo(ifExp, NonFoldableLiteral(true)))
val nonFoldable = If(NonFoldableLiteral(true), Literal(1), Literal(2))
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@cloud-fan cloud-fan Dec 16, 2020

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NonFoldableLiteral is nothing special comparing to 'a == 100, as they are both non-foldable. I think we don't need to test with NonFoldableLiteral

assertEquivalent(EqualTo(nonFoldable, Literal(1)), EqualTo(nonFoldable, Literal(1)))

// Do not simplify if it contains non-deterministic expressions.
val nonDeterministic = If(LessThan(Rand(1), Literal(0.5)), Literal(1), Literal(1))
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@cloud-fan cloud-fan Dec 16, 2020

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This is a case that we should optimize. But we need to distinguish between non-deterministic and has-side-effect. While we can skip running non-deterministic expressions, we can't skip running has-side-effect expressions.

This is not related to this PR, but is something worth considering. cc @viirya @dbtsai @maropu @rednaxelafx

assert(!nonDeterministic.deterministic)
assertEquivalent(EqualTo(nonDeterministic, Literal(-1)), EqualTo(nonDeterministic, Literal(-1)))

// null check, SPARK-33798 will change the following two behaviors.
assertEquivalent(
EqualTo(If(a === Literal(1), Literal(null, IntegerType), Literal(1)), Literal(2)),
FalseLiteral)
assertEquivalent(
EqualTo(If(a =!= Literal(1), Literal(1), Literal(2)), Literal(null, IntegerType)),
FalseLiteral)

assertEquivalent(
EqualTo(If(a === Literal(1), Literal(null, IntegerType), Literal(1)), Literal(1)),
EqualTo(If(a === Literal(1), Literal(null, IntegerType), Literal(1)), Literal(1)))
assertEquivalent(
EqualTo(If(a =!= Literal(1), Literal(null, IntegerType), Literal(1)), Literal(1)),
EqualTo(If(a =!= Literal(1), Literal(null, IntegerType), Literal(1)), Literal(1)))
assertEquivalent(
EqualTo(If(a =!= Literal(1), Literal(null, IntegerType), Literal(null, IntegerType)),
Literal(1)),
Literal(null, BooleanType))
}

test("SPARK-33798: simplify EqualTo(CaseWhen, Literal) always false") {
val a = EqualTo(UnresolvedAttribute("a"), Literal(100))
val b = UnresolvedAttribute("b")
val c = EqualTo(UnresolvedAttribute("c"), Literal(true))
val caseWhen = CaseWhen(Seq((a, Literal(1)), (c, Literal(2))), Some(Literal(3)))

assertEquivalent(EqualTo(caseWhen, Literal(4)), FalseLiteral)
assertEquivalent(EqualTo(caseWhen, Literal(3)), EqualTo(caseWhen, Literal(3)))
assertEquivalent(EqualTo(caseWhen, Literal("4")), FalseLiteral)
assertEquivalent(EqualTo(caseWhen, Literal("3")), EqualTo(caseWhen, Literal(3)))
assertEquivalent(
EqualTo(CaseWhen(Seq((a, Literal("1")), (c, Literal("2"))), None), Literal("4")),
FalseLiteral)

assertEquivalent(
And(EqualTo(caseWhen, Literal(5)), EqualTo(caseWhen, Literal(6))),
FalseLiteral)

assertEquivalent(
EqualTo(CaseWhen(Seq(normalBranch, (a, Literal(1)), (c, Literal(1))), None), Literal(-1)),
FalseLiteral)

// Do not simplify if it contains non foldable expressions.
assertEquivalent(EqualTo(caseWhen, NonFoldableLiteral(true)),
EqualTo(caseWhen, NonFoldableLiteral(true)))
val nonFoldable = CaseWhen(Seq(normalBranch, (a, b)), None)
assertEquivalent(EqualTo(nonFoldable, Literal(1)), EqualTo(nonFoldable, Literal(1)))

// Do not simplify if it contains non-deterministic expressions.
val nonDeterministic = CaseWhen(Seq((LessThan(Rand(1), Literal(0.5)), Literal(1))), Some(b))
assert(!nonDeterministic.deterministic)
assertEquivalent(EqualTo(nonDeterministic, Literal(-1)), EqualTo(nonDeterministic, Literal(-1)))

// null check, SPARK-33798 will change the following two behaviors.
assertEquivalent(
EqualTo(CaseWhen(Seq((a, Literal(null, IntegerType))), Some(Literal(1))), Literal(2)),
FalseLiteral)
assertEquivalent(
EqualTo(CaseWhen(Seq((a, Literal(1))), Some(Literal(2))), Literal(null, IntegerType)),
FalseLiteral)
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@wangyum wangyum Dec 16, 2020

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SPARK-33798 will change these behaviors as expected.


assertEquivalent(
EqualTo(CaseWhen(Seq((a, Literal(null, IntegerType))), Some(Literal(1))), Literal(1)),
EqualTo(CaseWhen(Seq((a, Literal(null, IntegerType))), Some(Literal(1))), Literal(1)))
assertEquivalent(
EqualTo(CaseWhen(Seq((a, Literal(null, IntegerType))), Some(Literal(null, IntegerType))),
Literal(1)),
Literal(null, BooleanType))
assertEquivalent(
EqualTo(CaseWhen(Seq((a, Literal(null, IntegerType))), Some(Literal(null, IntegerType))),
Literal(null, IntegerType)),
Literal(null, BooleanType))
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@wangyum wangyum Dec 16, 2020

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SPARK-33798 will not change these behaviors.

}
}