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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.AnalysisException
import org.apache.spark.sql.catalyst.expressions._
import org.apache.spark.sql.types._
/**
* Returns the first value of `child` for a group of rows. If the first value of `child`
* is `null`, it returns `null` (respecting nulls). Even if [[First]] is used on a already
* sorted column, if we do partial aggregation and final aggregation (when mergeExpression
* is used) its result will not be deterministic (unless the input table is sorted and has
* a single partition, and we use a single reducer to do the aggregation.).
*/
case class First(child: Expression, ignoreNullsExpr: Expression) extends DeclarativeAggregate {
def this(child: Expression) = this(child, Literal.create(false, BooleanType))
private val ignoreNulls: Boolean = ignoreNullsExpr match {
case Literal(b: Boolean, BooleanType) => b
case _ =>
throw new AnalysisException("The second argument of First should be a boolean literal.")
}
override def children: Seq[Expression] = child :: Nil
override def nullable: Boolean = true
// First is not a deterministic function.
override def deterministic: Boolean = false
// Return data type.
override def dataType: DataType = child.dataType
// Expected input data type.
override def inputTypes: Seq[AbstractDataType] = Seq(AnyDataType)
private lazy val first = AttributeReference("first", child.dataType)()
private lazy val valueSet = AttributeReference("valueSet", BooleanType)()
override lazy val aggBufferAttributes: Seq[AttributeReference] = first :: valueSet :: Nil
override lazy val initialValues: Seq[Literal] = Seq(
/* first = */ Literal.create(null, child.dataType),
/* valueSet = */ Literal.create(false, BooleanType)
)
override lazy val updateExpressions: Seq[Expression] = {
if (ignoreNulls) {
Seq(
/* first = */ If(Or(valueSet, IsNull(child)), first, child),
/* valueSet = */ Or(valueSet, IsNotNull(child))
)
} else {
Seq(
/* first = */ If(valueSet, first, child),
/* valueSet = */ Literal.create(true, BooleanType)
)
}
}
override lazy val mergeExpressions: Seq[Expression] = {
// For first, we can just check if valueSet.left is set to true. If it is set
// to true, we use first.right. If not, we use first.right (even if valueSet.right is
// false, we are safe to do so because first.right will be null in this case).
Seq(
/* first = */ If(valueSet.left, first.left, first.right),
/* valueSet = */ Or(valueSet.left, valueSet.right)
)
}
override lazy val evaluateExpression: AttributeReference = first
override def toString: String = s"first($child)${if (ignoreNulls) " ignore nulls"}"
}
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