Github user mn-mikke commented on a diff in the pull request: https://github.com/apache/spark/pull/22017#discussion_r208280351 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/higherOrderFunctions.scala --- @@ -365,3 +364,101 @@ case class ArrayAggregate( override def prettyName: String = "aggregate" } + +/** + * Merges two given maps into a single map by applying function to the pair of values with + * the same key. + */ +@ExpressionDescription( + usage = + """ + _FUNC_(map1, map2, function) - Merges two given maps into a single map by applying + function to the pair of values with the same key. For keys only presented in one map, + NULL will be passed as the value for the missing key. If an input map contains duplicated + keys, only the first entry of the duplicated key is passed into the lambda function. + """, + examples = """ + Examples: + > SELECT _FUNC_(map(1, 'a', 2, 'b'), map(1, 'x', 2, 'y'), (k, v1, v2) -> concat(v1, v2)); + {1:"ax",2:"by"} + """, + since = "2.4.0") +case class MapZipWith(left: Expression, right: Expression, function: Expression) + extends HigherOrderFunction with CodegenFallback { + + @transient lazy val functionForEval: Expression = functionsForEval.head + + @transient lazy val MapType(keyType, leftValueType, _) = getMapType(left) + + @transient lazy val MapType(_, rightValueType, _) = getMapType(right) + + @transient lazy val arrayDataUnion = new ArrayDataUnion(keyType) + + @transient lazy val ordering = TypeUtils.getInterpretedOrdering(keyType) + + override def inputs: Seq[Expression] = left :: right :: Nil + + override def functions: Seq[Expression] = function :: Nil + + override def nullable: Boolean = left.nullable || right.nullable --- End diff -- ```nullable``` flag is rather related to the cases when the whole map is ```null```. The case that you are referring to is handled by ```valueContainsNull``` flag of ```MapType``` (see the line [423](https://github.com/apache/spark/pull/22017/files/ec583eb29ba6fdb79d0b85cbecb3f709e6648b25#diff-ef52827ed9b41efc1fbd056a06ef7c6aR423)).
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