Github user davies commented on a diff in the pull request:
https://github.com/apache/spark/pull/10960#discussion_r51535532
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/misc.scala
---
@@ -436,3 +436,21 @@ case class Murmur3Hash(children: Seq[Expression],
seed: Int) extends Expression
}
}
}
+
+/**
+ * An expression that will print the value of child to stderr (used for
debugging codegen).
+ */
+case class Echo(child: Expression) extends UnaryExpression {
--- End diff --
This could be used to print out the the result of any expression, for
example
```
Sqrt(Echo(a * b))
```
You can see the result of `a * b`
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