[SPARK-27653][SQL] Add max_by() and min_by() SQL aggregate functions

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/FunctionRegistry.scala

@@ -289,8 +289,10 @@ object FunctionRegistry {
     expression[Last]("last"),
     expression[Last]("last_value"),
     expression[Max]("max"),
+    expression[MaxBy]("max_by"),
     expression[Average]("mean"),
     expression[Min]("min"),
+    expression[MinBy]("min_by"),
     expression[Percentile]("percentile"),
     expression[Skewness]("skewness"),
     expression[ApproximatePercentile]("percentile_approx"),

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/MaxByAndMinBy.scala

@@ -0,0 +1,128 @@
+/*
+ * 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._
+
+/**
+ * The shared abstract superclass for `MaxBy` and `MinBy` SQL aggregate functions.
+ */
+abstract class MaxMinBy extends DeclarativeAggregate {
+
+  def valueExpr: Expression
+  def orderingExpr: Expression
+
+  protected def funcName: String
+  // The predicate compares two ordering values.
+  protected def predicate(oldExpr: Expression, newExpr: Expression): Expression
+  // The arithmetic expression returns greatest/least value of all parameters.
+  // Used to pick up updated ordering value.
+  protected def orderingUpdater(oldExpr: Expression, newExpr: Expression): Expression
+
+  override def children: Seq[Expression] = valueExpr :: orderingExpr :: Nil
+
+  override def nullable: Boolean = true
+
+  // Return data type.
+  override def dataType: DataType = valueExpr.dataType
+
+  override def checkInputDataTypes(): TypeCheckResult =
+    TypeUtils.checkForOrderingExpr(orderingExpr.dataType, s"function $funcName")
+
+  // The attributes used to keep extremum (max or min) and associated aggregated values.
+  private lazy val extremumOrdering =
+    AttributeReference("extremumOrdering", orderingExpr.dataType)()
+  private lazy val valueWithExtremumOrdering =
+    AttributeReference("valueWithExtremumOrdering", valueExpr.dataType)()
+
+  override lazy val aggBufferAttributes: Seq[AttributeReference] =
+    valueWithExtremumOrdering :: extremumOrdering :: Nil
+
+  private lazy val nullValue = Literal.create(null, valueExpr.dataType)
+  private lazy val nullOrdering = Literal.create(null, orderingExpr.dataType)
+
+  override lazy val initialValues: Seq[Literal] = Seq(
+    /* valueWithExtremumOrdering = */ nullValue,
+    /* extremumOrdering = */ nullOrdering
+  )
+
+  override lazy val updateExpressions: Seq[Expression] = Seq(
+    /* valueWithExtremumOrdering = */
+    CaseWhen(
+      (extremumOrdering.isNull && orderingExpr.isNull, nullValue) ::
+        (extremumOrdering.isNull, valueExpr) ::
+        (orderingExpr.isNull, valueWithExtremumOrdering) :: Nil,
+      If(predicate(extremumOrdering, orderingExpr), valueWithExtremumOrdering, valueExpr)
+    ),
+    /* extremumOrdering = */ orderingUpdater(extremumOrdering, orderingExpr)
+  )
+
+  override lazy val mergeExpressions: Seq[Expression] = Seq(
+    /* valueWithExtremumOrdering = */
+    CaseWhen(
+      (extremumOrdering.left.isNull && extremumOrdering.right.isNull, nullValue) ::
+        (extremumOrdering.left.isNull, valueWithExtremumOrdering.right) ::
+        (extremumOrdering.right.isNull, valueWithExtremumOrdering.left) :: Nil,
+      If(predicate(extremumOrdering.left, extremumOrdering.right),
+        valueWithExtremumOrdering.left, valueWithExtremumOrdering.right)
+    ),
+    /* extremumOrdering = */ orderingUpdater(extremumOrdering.left, extremumOrdering.right)
+  )
+
+  override lazy val evaluateExpression: AttributeReference = valueWithExtremumOrdering
+}
+
+@ExpressionDescription(
+  usage = "_FUNC_(x, y) - Returns the value of `x` associated with the maximum value of `y`.",
+  examples = """
+    Examples:
+      > SELECT _FUNC_(x, y) FROM VALUES (('a', 10)), (('b', 50)), (('c', 20)) AS tab(x, y);
+       b
+  """,
+  since = "3.0")
+case class MaxBy(valueExpr: Expression, orderingExpr: Expression) extends MaxMinBy {
+  override protected def funcName: String = "max_by"
+
+  override protected def predicate(oldExpr: Expression, newExpr: Expression): Expression =
+    oldExpr > newExpr
+
+  override protected def orderingUpdater(oldExpr: Expression, newExpr: Expression): Expression =
+    greatest(oldExpr, newExpr)
+}
+
+@ExpressionDescription(
+  usage = "_FUNC_(x, y) - Returns the value of `x` associated with the minimum value of `y`.",
+  examples = """
+    Examples:
+      > SELECT _FUNC_(x, y) FROM VALUES (('a', 10)), (('b', 50)), (('c', 20)) AS tab(x, y);
+       a
+  """,
+  since = "3.0")
+case class MinBy(valueExpr: Expression, orderingExpr: Expression) extends MaxMinBy {
+  override protected def funcName: String = "min_by"
+
+  override protected def predicate(oldExpr: Expression, newExpr: Expression): Expression =
+    oldExpr < newExpr
+
+  override protected def orderingUpdater(oldExpr: Expression, newExpr: Expression): Expression =
+    least(oldExpr, newExpr)
+}

sql/core/src/test/scala/org/apache/spark/sql/DataFrameAggregateSuite.scala

@@ -782,4 +782,116 @@ class DataFrameAggregateSuite extends QueryTest with SharedSQLContext {
     val countAndDistinct = df.select(count("*"), countDistinct("*"))
     checkAnswer(countAndDistinct, Row(100000, 100))
   }
+
+  test("max_by") {
+    val yearOfMaxEarnings =
+      sql("SELECT course, max_by(year, earnings) FROM courseSales GROUP BY course")
+    checkAnswer(yearOfMaxEarnings, Row("dotNET", 2013) :: Row("Java", 2013) :: Nil)
+
+    checkAnswer(
+      sql("SELECT max_by(x, y) FROM VALUES (('a', 10)), (('b', 50)), (('c', 20)) AS tab(x, y)"),
+      Row("b") :: Nil
+    )
+
+    checkAnswer(
+      sql("SELECT max_by(x, y) FROM VALUES (('a', 10)), (('b', null)), (('c', 20)) AS tab(x, y)"),
+      Row("c") :: Nil
+    )
+
+    checkAnswer(
+      sql("SELECT max_by(x, y) FROM VALUES (('a', null)), (('b', null)), (('c', 20)) AS tab(x, y)"),
+      Row("c") :: Nil
+    )
+
+    checkAnswer(
+      sql("SELECT max_by(x, y) FROM VALUES (('a', 10)), (('b', 50)), (('c', null)) AS tab(x, y)"),
+      Row("b") :: Nil
+    )
+
+    checkAnswer(
+      sql("SELECT max_by(x, y) FROM VALUES (('a', null)), (('b', null)) AS tab(x, y)"),
+      Row(null) :: Nil
+    )
+
+    // structs as ordering value.
+    checkAnswer(
+      sql("select max_by(x, y) FROM VALUES (('a', (10, 20))), (('b', (10, 50))), " +
+        "(('c', (10, 60))) AS tab(x, y)"),
+      Row("c") :: Nil
+    )
+
+    checkAnswer(
+      sql("select max_by(x, y) FROM VALUES (('a', (10, 20))), (('b', (10, 50))), " +
+        "(('c', null)) AS tab(x, y)"),
+      Row("b") :: Nil
+    )
+
+    withTempView("tempView") {
+      val dfWithMap = Seq((0, "a"), (1, "b"), (2, "c"))
+        .toDF("x", "y")
+        .select($"x", map($"x", $"y").as("y"))
+        .createOrReplaceTempView("tempView")
+      val error = intercept[AnalysisException] {
+        sql("SELECT max_by(x, y) FROM tempView").show
+      }
+      assert(
+        error.message.contains("function max_by does not support ordering on type map<int,string>"))
+    }
+  }
+
+  test("min_by") {
+    val yearOfMinEarnings =
+      sql("SELECT course, min_by(year, earnings) FROM courseSales GROUP BY course")
+    checkAnswer(yearOfMinEarnings, Row("dotNET", 2012) :: Row("Java", 2012) :: Nil)
+
+    checkAnswer(
+      sql("SELECT min_by(x, y) FROM VALUES (('a', 10)), (('b', 50)), (('c', 20)) AS tab(x, y)"),
+      Row("a") :: Nil
+    )
+
+    checkAnswer(
+      sql("SELECT min_by(x, y) FROM VALUES (('a', 10)), (('b', null)), (('c', 20)) AS tab(x, y)"),
+      Row("a") :: Nil
+    )
+
+    checkAnswer(
+      sql("SELECT min_by(x, y) FROM VALUES (('a', null)), (('b', null)), (('c', 20)) AS tab(x, y)"),
+      Row("c") :: Nil
+    )
+
+    checkAnswer(
+      sql("SELECT min_by(x, y) FROM VALUES (('a', 10)), (('b', 50)), (('c', null)) AS tab(x, y)"),
+      Row("a") :: Nil
+    )
+
+    checkAnswer(
+      sql("SELECT min_by(x, y) FROM VALUES (('a', null)), (('b', null)) AS tab(x, y)"),
+      Row(null) :: Nil
+    )
+
+    // structs as ordering value.
+    checkAnswer(
+      sql("select min_by(x, y) FROM VALUES (('a', (10, 20))), (('b', (10, 50))), " +
+        "(('c', (10, 60))) AS tab(x, y)"),
+      Row("a") :: Nil
+    )
+
+    checkAnswer(
+      sql("select min_by(x, y) FROM VALUES (('a', null)), (('b', (10, 50))), " +
+        "(('c', (10, 60))) AS tab(x, y)"),
+      Row("b") :: Nil
+    )
+
+    withTempView("tempView") {
+      val dfWithMap = Seq((0, "a"), (1, "b"), (2, "c"))
+        .toDF("x", "y")
+        .select($"x", map($"x", $"y").as("y"))
+        .createOrReplaceTempView("tempView")
+      val error = intercept[AnalysisException] {
+        sql("SELECT min_by(x, y) FROM tempView").show
+      }
+      assert(
+        error.message.contains("function min_by does not support ordering on type map<int,string>"))
+    }
+  }
 }