Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/22957#discussion_r237065506
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala
---
@@ -195,14 +195,26 @@ abstract class Expression extends
TreeNode[Expression] {
}
/**
- * Returns true when two expressions will always compute the same
result, even if they differ
+ * Returns true when two expressions will always compute the same
output, even if they differ
* cosmetically (i.e. capitalization of names in attributes may be
different).
*
* See [[Canonicalize]] for more details.
*/
def semanticEquals(other: Expression): Boolean =
deterministic && other.deterministic && canonicalized ==
other.canonicalized
+ /**
+ * Returns true when two expressions will always compute the same
result, even if the output may
+ * be different, because of different names or similar differences.
+ * Usually this means they their canonicalized form equals, but it may
also not be the case, as
+ * different output expressions can evaluate to the same result as well
(eg. when an expression
+ * is aliased).
+ */
+ def sameResult(other: Expression): Boolean = other match {
--- End diff --
"erase the name" can also mean remove `Alias`. If we can't clearly tell the
difference between `semanticEquals` and `sameResult`, and give a guideline
about using which one in which case, I think we should just update
`semanticEquals`(i.e. `Canonicalize`).
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