cloud-fan commented on a change in pull request #35213:
URL: https://github.com/apache/spark/pull/35213#discussion_r785718131
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala
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@@ -366,6 +366,8 @@ trait RuntimeReplaceable extends UnaryExpression with
Unevaluable {
// are semantically equal.
override lazy val preCanonicalized: Expression = child.preCanonicalized
+ def isAggregate: Boolean = child.isInstanceOf[AggregateFunction]
Review comment:
More thoughts about it: technically a `RuntimeReplaceable` can combine
one or more expressions, even for something like `f(x) = max(x) - min(x)`.
For aggregate functions, it's very hard to reason about `f(distinct x)
FILTER WHERE ...` if `f(x)` combines many expressions, so I think it makes
sense to only allow a direct mapping here.
We can make this assumption more explicit here
```
def isAggregate: Boolean = {
if (child.isInstanceOf[AggregateFunction]) {
true
} else {
assert(child.find(_.isInstanceOf[AggregateFunction]).isEmpty)
false
}
}
```
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