Github user dilipbiswal commented on a diff in the pull request:
https://github.com/apache/spark/pull/22809#discussion_r228666789
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/UnevaluableAggs.scala
---
@@ -0,0 +1,62 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
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+ * See the License for the specific language governing permissions and
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+ */
+
+package org.apache.spark.sql.catalyst.expressions.aggregate
+
+import org.apache.spark.sql.catalyst.analysis.TypeCheckResult
+import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.types._
+
+abstract class UnevaluableBooleanAggBase(arg: Expression)
--- End diff --
@mgaido91 I re-read your comments again and here is what i think you are
implying :
1. In UnevaluableAggregate, define a method say `replacedExpression`
2. The sub-class overrides it and return an actual rewritten expression
3. In optimized, match UnevaluableAggregate and call `replacedExpression`
Did i understand it correctly ? If so, actually, i wouldn't prefer that
way. The reason is, the replacedExpression is hidden from analyzer and so it
may not be safe. The way ReplaceExpression framework is nicely designed, the
analyzer resolves the rewritten expression normally (as its the child
expression). Thats the reason, i have opted for specific/targeted rewrites.
If Wenchen and you think otherwise, then i can change.
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