Github user mn-mikke commented on a diff in the pull request:
https://github.com/apache/spark/pull/22017#discussion_r209876913
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/higherOrderFunctions.scala
---
@@ -496,3 +496,194 @@ 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 {
+
+ def functionForEval: Expression = functionsForEval.head
+
+ @transient lazy val MapType(leftKeyType, leftValueType,
leftValueContainsNull) = left.dataType
+
+ @transient lazy val MapType(rightKeyType, rightValueType,
rightValueContainsNull) = right.dataType
+
+ @transient lazy val keyType =
+ TypeCoercion.findCommonTypeDifferentOnlyInNullFlags(leftKeyType,
rightKeyType).get
--- End diff --
If ```leftKeyType``` is ```ArrayType(IntegerType, false)``` and
```rightKeyType``` is ```ArrayType(IntegerType, true)``` for instance, the
coercion rule is not executed ```leftKeyType.sameType(rightKeyType) == true```.
An array with nulls seems to be a valid key.:
```
scala> spark.range(1).selectExpr("map(array(1, 2, null), 12)").show()
+---------------------------------------+
|map(array(1, 2, CAST(NULL AS INT)), 12)|
+---------------------------------------+
| [[1, 2,] -> 12]|
+---------------------------------------+
```
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