viirya commented on a change in pull request #32559:
URL: https://github.com/apache/spark/pull/32559#discussion_r634106098
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala
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@@ -82,21 +82,31 @@ class EquivalentExpressions {
/**
* Adds only expressions which are common in each of given expressions, in a
recursive way.
* For example, given two expressions `(a + (b + (c + 1)))` and `(d + (e +
(c + 1)))`,
- * the common expression `(c + 1)` will be added into `equivalenceMap`.
+ * the common expression `(c + 1)` will be added into `equivalenceMap`. Note
that if an
+ * expression and its child expressions are all commonly occurred in each of
given expressions,
+ * we filter out the child expressions. For example, if `((a + b) + c)` and
`(a + b)` are
+ * common expressions, we only add `((a + b) + c)`.
Review comment:
Updated the comment.
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