HyukjinKwon commented on a change in pull request #34883:
URL: https://github.com/apache/spark/pull/34883#discussion_r768251362
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala
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@@ -222,6 +222,20 @@ abstract class Expression extends TreeNode[Expression] {
*/
def childrenResolved: Boolean = children.forall(_.resolved)
+ // Return a roughly canonicalized expression, which recursively
canonicalizes each expression node
+ // without changing the structure of the expression tree.
+ // This method should only be called in `canonicalized` or subclass's
`roughlyCanonicalized`.
+ // Subclasses (especially leaf nodes) should override this method to
customize the
+ // canonicalization logic. Some basic canonicalization rules:
+ // - Names and nullability hints for `DataType`s are stripped. See the
override in
+ // `AttributeReference` and `GetStructField`.
+ // - TimeZoneId for [[Cast]] and [[AnsiCast]] are stripped if
`needsTimeZone` is false.
+ // - Rearrange the inputs of certain predicate expressions according to the
`hashCode` of inputs.
+ lazy val roughlyCanonicalized: Expression = {
Review comment:
Yeah .. or `fastCanonicalized`?
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