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[SPARK-31166][SQL] UNION map<null, null> and other maps should not fail #27926

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[SPARK-31166][SQL] UNION map<null, null> and other maps should not fail #27926

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2 changes: 1 addition & 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 @@ -158,7 +158,7 @@ object TypeCoercion {
}
case (MapType(kt1, vt1, valueContainsNull1), MapType(kt2, vt2, valueContainsNull2)) =>
findTypeFunc(kt1, kt2)
.filter { kt => !Cast.forceNullable(kt1, kt) && !Cast.forceNullable(kt2, kt) }
.filter { kt => Cast.canCastMapKeyNullSafe(kt1, kt) && Cast.canCastMapKeyNullSafe(kt2, kt) }
.flatMap { kt =>
findTypeFunc(vt1, vt2).map { vt =>
MapType(kt, vt, valueContainsNull1 || valueContainsNull2 ||
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8 changes: 6 additions & 2 deletions sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
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Expand Up @@ -77,8 +77,7 @@ object Cast {
resolvableNullability(fn || forceNullable(fromType, toType), tn)

case (MapType(fromKey, fromValue, fn), MapType(toKey, toValue, tn)) =>
canCast(fromKey, toKey) &&
(!forceNullable(fromKey, toKey)) &&
canCast(fromKey, toKey) && canCastMapKeyNullSafe(fromKey, toKey) &&
canCast(fromValue, toValue) &&
resolvableNullability(fn || forceNullable(fromValue, toValue), tn)

Expand All @@ -98,6 +97,11 @@ object Cast {
case _ => false
}

def canCastMapKeyNullSafe(fromType: DataType, toType: DataType): Boolean = {
// If the original map key type is NullType, it's OK as the map must be empty.
fromType == NullType || !forceNullable(fromType, toType)
}

/**
* Return true if we need to use the `timeZone` information casting `from` type to `to` type.
* The patterns matched reflect the current implementation in the Cast node.
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6 changes: 6 additions & 0 deletions sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala
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Expand Up @@ -3487,6 +3487,12 @@ class SQLQuerySuite extends QueryTest with SharedSparkSession with AdaptiveSpark
}
}
}

test("SPARK-31166: UNION map<null, null> and other maps should not fail") {
checkAnswer(
sql("(SELECT map()) UNION ALL (SELECT map(1, 2))"),
Seq(Row(Map[Int, Int]()), Row(Map(1 -> 2))))
}
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@maropu maropu Mar 17, 2020

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Nice catch! It seems #27542 broke some other queries merging map<null,null> and map<some type, some type>, e.g., map_concat;

// the current master
scala> sql("select map_concat(map(), map(1, 2))").show()
org.apache.spark.sql.AnalysisException: cannot resolve 'map_concat(map(), map(1, 2))' due to data type mismatch: input to function map_concat should all be the same type, but it's [map<null,null>, map<int,int>]; line 1 pos 7;
'Project [unresolvedalias(map_concat(map(), map(1, 2)), None)]
+- OneRowRelation

  at org.apache.spark.sql.catalyst.analysis.package$AnalysisErrorAt.failAnalysis(package.scala:42)

This PR can fix this query, too.

}

case class Foo(bar: Option[String])