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/*
* 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.analysis.TypeCheckResult
import org.apache.spark.sql.catalyst.dsl.expressions._
import org.apache.spark.sql.catalyst.expressions._
import org.apache.spark.sql.catalyst.util.TypeUtils
import org.apache.spark.sql.types._
@ExpressionDescription(
usage = "_FUNC_(x) - Returns the mean calculated from values of a group.")
case class Average(child: Expression) extends DeclarativeAggregate {
override def prettyName: String = "avg"
override def children: Seq[Expression] = child :: Nil
override def nullable: Boolean = true
// Return data type.
override def dataType: DataType = resultType
override def inputTypes: Seq[AbstractDataType] = Seq(NumericType)
override def checkInputDataTypes(): TypeCheckResult =
TypeUtils.checkForNumericExpr(child.dataType, "function average")
private lazy val resultType = child.dataType match {
case DecimalType.Fixed(p, s) =>
DecimalType.bounded(p + 4, s + 4)
case _ => DoubleType
}
private lazy val sumDataType = child.dataType match {
case _ @ DecimalType.Fixed(p, s) => DecimalType.bounded(p + 10, s)
case _ => DoubleType
}
private lazy val sum = AttributeReference("sum", sumDataType)()
private lazy val count = AttributeReference("count", LongType)()
override lazy val aggBufferAttributes = sum :: count :: Nil
override lazy val initialValues = Seq(
/* sum = */ Cast(Literal(0), sumDataType),
/* count = */ Literal(0L)
)
override lazy val updateExpressions = Seq(
/* sum = */
Add(
sum,
Coalesce(Cast(child, sumDataType) :: Cast(Literal(0), sumDataType) :: Nil)),
/* count = */ If(IsNull(child), count, count + 1L)
)
override lazy val mergeExpressions = Seq(
/* sum = */ sum.left + sum.right,
/* count = */ count.left + count.right
)
// If all input are nulls, count will be 0 and we will get null after the division.
override lazy val evaluateExpression = child.dataType match {
case DecimalType.Fixed(p, s) =>
// increase the precision and scale to prevent precision loss
val dt = DecimalType.bounded(p + 14, s + 4)
Cast(Cast(sum, dt) / Cast(count, dt), resultType)
case _ =>
Cast(sum, resultType) / Cast(count, resultType)
}
}
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