Github user chenghao-intel commented on a diff in the pull request:
https://github.com/apache/spark/pull/482#discussion_r12125494
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala
---
@@ -223,6 +222,11 @@ abstract class Expression extends TreeNode[Expression]
{
}
}
+/**
+ * Root class for rewritten 2 operands UDF expression. By default, we
assume it produces Null if
+ * either one of its operands is null. Exceptional case requires to update
the optimization rule
+ * at [[optimizer.ConstantFolding ConstantFolding]]
+ */
abstract class BinaryExpression extends Expression with
trees.BinaryNode[Expression] {
--- End diff --
That's true, adding document restrictions for BinaryExpression /
UnaryExpression is quite confusing and error-prone. Besides the
BinaryArithmetic, also the rewrite UDFs RLike / Cast / BinaryComparison
etc.will be considered, too.
Probably enumerate all of the expression types in this rule makes more
sense.
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