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[SPARK-21811][SQL] Fix the inconsistency behavior when finding the widest common type #21074

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jiangxb1987 wants to merge 7 commits into from
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[SPARK-21811][SQL] Fix the inconsistency behavior when finding the widest common type #21074

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803a6a4
fix type coercion when promting to StringType
jiangxb1987 Apr 15, 2018
571912f
refactor and update migration guide.
jiangxb1987 Apr 17, 2018
d77f213
update comments
jiangxb1987 Apr 17, 2018
4ce5081
fix also for array types
jiangxb1987 Apr 18, 2018
55eefe0
refactor
jiangxb1987 Apr 18, 2018
c2abce2
update comments
jiangxb1987 Apr 18, 2018
ff514af
update migration guide
jiangxb1987 Apr 18, 2018
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8 changes: 7 additions & 1 deletion sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -178,7 +178,13 @@ object TypeCoercion {
private def findWiderCommonType(types: Seq[DataType]): Option[DataType] = {
types.foldLeft[Option[DataType]](Some(NullType))((r, c) => r match {
case Some(d) => findWiderTypeForTwo(d, c)
case None => None
// Currently we find the wider common type by comparing the two types from left to right,
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@cloud-fan cloud-fan Apr 16, 2018

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The real problem is, findWiderTypeForTwo doesn't satisfy the associative law, i.e. (a op b) op c may not equal to a op (b op c). I think StringType is the only exception here, it's more clear to do

val (stringType, nonStringType) = types.partition(_ == StringType)
(stringType.distinct ++ nonStringType).foldLeft...

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@gatorsmile gatorsmile Apr 16, 2018

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This is a behavior change. We need to make it configurable. Add a conf and update the migration guide.

// this can be a problem when you have two data types which don't have a common type but each
// can be promoted to StringType. For instance, (TimestampType, IntegerType, StringType)
// should have StringType as the wider common type.
case None if types.exists(_ == StringType) &&
types.forall(stringPromotion(_, StringType).nonEmpty) => Some(StringType)
case _ => None
})
}

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5 changes: 5 additions & 0 deletions sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercionSuite.scala
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Expand Up @@ -572,6 +572,11 @@ class TypeCoercionSuite extends AnalysisTest {
Coalesce(Seq(nullLit, floatNullLit, doubleLit, stringLit)),
Coalesce(Seq(Cast(nullLit, StringType), Cast(floatNullLit, StringType),
Cast(doubleLit, StringType), Cast(stringLit, StringType))))

ruleTest(rule,
Coalesce(Seq(timestampLit, intLit, stringLit)),
Coalesce(Seq(Cast(timestampLit, StringType), Cast(intLit, StringType),
Cast(stringLit, StringType))))
}

test("CreateArray casts") {
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