Github user yhuai commented on a diff in the pull request:
https://github.com/apache/spark/pull/7458#discussion_r35726525
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/functions.scala
---
@@ -0,0 +1,292 @@
+/*
+ * 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
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.expressions.aggregate
+
+import org.apache.spark.sql.catalyst.dsl.expressions._
+import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.types._
+
+case class Average(child: Expression) extends AlgebraicAggregate {
+
+ override def children: Seq[Expression] = child :: Nil
+
+ override def nullable: Boolean = true
+
+ // Return data type.
+ override def dataType: DataType = resultType
+
+ // Expected input data type.
+ // TODO: Once we remove the old code path, we can use our analyzer to
cast NullType
+ // to the default data type of the NumericType.
+ override def inputTypes: Seq[AbstractDataType] =
Seq(TypeCollection(NumericType, NullType))
+
+ private val resultType = child.dataType match {
+ case DecimalType.Fixed(precision, scale) =>
+ DecimalType(precision + 4, scale + 4)
+ case DecimalType.Unlimited => DecimalType.Unlimited
+ case _ => DoubleType
+ }
+
+ private val sumDataType = child.dataType match {
+ case _ @ DecimalType() => DecimalType.Unlimited
+ case _ => DoubleType
+ }
+
+ private val currentSum = AttributeReference("currentSum", sumDataType)()
+ private val currentCount = AttributeReference("currentCount", LongType)()
+
+ override val bufferAttributes = currentSum :: currentCount :: Nil
+
+ override val initialValues = Seq(
+ /* currentSum = */ Cast(Literal(0), sumDataType),
+ /* currentCount = */ Literal(0L)
+ )
+
+ override val updateExpressions = Seq(
+ /* currentSum = */
+ Add(
+ currentSum,
+ Coalesce(Cast(child, sumDataType) :: Cast(Literal(0), sumDataType)
:: Nil)),
+ /* currentCount = */ If(IsNull(child), currentCount, currentCount + 1L)
+ )
+
+ override val mergeExpressions = Seq(
+ /* currentSum = */ currentSum.left + currentSum.right,
+ /* currentCount = */ currentCount.left + currentCount.right
+ )
+
+ // If all input are nulls, currentCount will be 0 and we will get null
after the division.
+ override val evaluateExpression = Cast(currentSum, resultType) /
Cast(currentCount, resultType)
+}
+
+case class Count(child: Expression) extends AlgebraicAggregate {
+ override def children: Seq[Expression] = child :: Nil
+
+ override def nullable: Boolean = false
+
+ // Return data type.
+ override def dataType: DataType = LongType
+
+ // Expected input data type.
+ override def inputTypes: Seq[AbstractDataType] = Seq(AnyDataType)
+
+ private val currentCount = AttributeReference("currentCount", LongType)()
+
+ override val bufferAttributes = currentCount :: Nil
+
+ override val initialValues = Seq(
+ /* currentCount = */ Literal(0L)
+ )
+
+ override val updateExpressions = Seq(
+ /* currentCount = */ If(IsNull(child), currentCount, currentCount + 1L)
+ )
+
+ override val mergeExpressions = Seq(
+ /* currentCount = */ currentCount.left + currentCount.right
+ )
+
+ override val evaluateExpression = Cast(currentCount, LongType)
+}
+
+case class First(child: Expression) extends AlgebraicAggregate {
+
+ override def children: Seq[Expression] = child :: Nil
+
+ override def nullable: Boolean = true
+
+ // First is not a deterministic function.
+ override def deterministic: Boolean = false
--- End diff --
@cloud-fan An `Aggregate` operator handles the project list by itself.
There is no Project on top of an `Aggregate` to generate results. So, the first
two rules you mentioned will not fire.
My question is why we do not need to handle non-deterministic aggregation
function specially and why should not use `deterministic` for an aggregate
function? Let's say we have a query `sqlContext.sql("select i, f, f, f from
(select i, first(j) as f, rand() from t group by i, rand()) tmp")` and let's
also assume project collapse works with `Aggregate`. It still makes sense to
evaluate first once instead of three times, right? It is probably true that
`first` will give you the same answer even if you call it three times, but what
about other non-deterministic aggregate functions? Regarding predicate
pushdown, we cannot pushdown predicates using the result of an aggregate
function through an aggregate operator, right?
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