Github user mn-mikke commented on a diff in the pull request:
https://github.com/apache/spark/pull/21103#discussion_r205806876
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala
---
@@ -3805,3 +3799,233 @@ object ArrayUnion {
new GenericArrayData(arrayBuffer)
}
}
+
+/**
+ * Returns an array of the elements in the intersect of x and y, without
duplicates
+ */
+@ExpressionDescription(
+ usage = """
+ _FUNC_(array1, array2) - Returns an array of the elements in array1 but
not in array2,
+ without duplicates.
+ """,
+ examples = """
+ Examples:
+ > SELECT _FUNC_(array(1, 2, 3), array(1, 3, 5));
+ array(2)
+ """,
+ since = "2.4.0")
+case class ArrayExcept(left: Expression, right: Expression) extends
ArraySetLike {
--- End diff --
Maybe I'm missing something, but why we need to apply these checks if there
won't be any ```null``` flag merging performed?
If ```left.dataType``` and ```right.dataType``` are different, will be
casted according to the ```ImplicitTypeCasts``` coercion rule. If they differ
only in ```null``` flags, ```left.dataType``` could be directly returned since
there won't be any array elements from ```right``` present in the result.
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