[SPARK-17616][SQL] Support a single distinct aggregate combined with a non-partial aggregate

## What changes were proposed in this pull request?
We currently cannot execute an aggregate that contains a single distinct aggregate function and an one or more non-partially plannable aggregate functions, for example:
```sql
select   grp,
         collect_list(col1),
         count(distinct col2)
from     tbl_a
group by 1
```
This is a regression from Spark 1.6. This is caused by the fact that the single distinct aggregation code path assumes that all aggregates can be planned in two phases (is partially aggregatable). This PR works around this issue by triggering the `RewriteDistinctAggregates` in such cases (this is similar to the approach taken in 1.6).

## How was this patch tested?
Created `RewriteDistinctAggregatesSuite` which checks if the aggregates with distinct aggregate functions get rewritten into two `Aggregates` and an `Expand`. Added a regression test to `DataFrameAggregateSuite`.

Author: Herman van Hovell <hvanhovell@databricks.com>

Closes #15187 from hvanhovell/SPARK-17616.

3 files changed, 111 insertions, 9 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/RewriteDistinctAggregates.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/RewriteDistinctAggregates.scala
index 0f43e7bb88..d6a39ecf53 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/RewriteDistinctAggregates.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/RewriteDistinctAggregates.scala
@@ -119,14 +119,16 @@ object RewriteDistinctAggregates extends Rule[LogicalPlan] {
       .filter(_.isDistinct)
       .groupBy(_.aggregateFunction.children.toSet)
 
-    // Aggregation strategy can handle the query with single distinct
-    if (distinctAggGroups.size > 1) {
+    // Check if the aggregates contains functions that do not support partial aggregation.
+    val existsNonPartial = aggExpressions.exists(!_.aggregateFunction.supportsPartial)
+
+    // Aggregation strategy can handle queries with a single distinct group and partial aggregates.
+    if (distinctAggGroups.size > 1 || (distinctAggGroups.size == 1 && existsNonPartial)) {
       // Create the attributes for the grouping id and the group by clause.
-      val gid =
-        new AttributeReference("gid", IntegerType, false)(isGenerated = true)
+      val gid = AttributeReference("gid", IntegerType, nullable = false)(isGenerated = true)
       val groupByMap = a.groupingExpressions.collect {
         case ne: NamedExpression => ne -> ne.toAttribute
-        case e => e -> new AttributeReference(e.sql, e.dataType, e.nullable)()
+        case e => e -> AttributeReference(e.sql, e.dataType, e.nullable)()
       }
       val groupByAttrs = groupByMap.map(_._2)
 
@@ -135,9 +137,7 @@ object RewriteDistinctAggregates extends Rule[LogicalPlan] {
       def patchAggregateFunctionChildren(
           af: AggregateFunction)(
           attrs: Expression => Expression): AggregateFunction = {
-        af.withNewChildren(af.children.map {
-          case afc => attrs(afc)
-        }).asInstanceOf[AggregateFunction]
+        af.withNewChildren(af.children.map(attrs)).asInstanceOf[AggregateFunction]
       }
 
       // Setup unique distinct aggregate children.
@@ -265,5 +265,5 @@ object RewriteDistinctAggregates extends Rule[LogicalPlan] {
     // NamedExpression. This is done to prevent collisions between distinct and regular aggregate
     // children, in this case attribute reuse causes the input of the regular aggregate to bound to
     // the (nulled out) input of the distinct aggregate.
-    e -> new AttributeReference(e.sql, e.dataType, true)()
+    e -> AttributeReference(e.sql, e.dataType, nullable = true)()
 }
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/RewriteDistinctAggregatesSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/RewriteDistinctAggregatesSuite.scala
new file mode 100644
index 0000000000..0b973c3b65
--- /dev/null
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/RewriteDistinctAggregatesSuite.scala
@@ -0,0 +1,94 @@
+/*
+ * 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.optimizer
+
+import org.apache.spark.sql.catalyst.SimpleCatalystConf
+import org.apache.spark.sql.catalyst.analysis.{Analyzer, EmptyFunctionRegistry}
+import org.apache.spark.sql.catalyst.catalog.{InMemoryCatalog, SessionCatalog}
+import org.apache.spark.sql.catalyst.dsl.expressions._
+import org.apache.spark.sql.catalyst.dsl.plans._
+import org.apache.spark.sql.catalyst.expressions.{If, Literal}
+import org.apache.spark.sql.catalyst.expressions.aggregate.{CollectSet, Count}
+import org.apache.spark.sql.catalyst.plans.PlanTest
+import org.apache.spark.sql.catalyst.plans.logical.{Aggregate, Expand, LocalRelation, LogicalPlan}
+import org.apache.spark.sql.types.{IntegerType, StringType}
+
+class RewriteDistinctAggregatesSuite extends PlanTest {
+  val conf = SimpleCatalystConf(caseSensitiveAnalysis = false, groupByOrdinal = false)
+  val catalog = new SessionCatalog(new InMemoryCatalog, EmptyFunctionRegistry, conf)
+  val analyzer = new Analyzer(catalog, conf)
+
+  val nullInt = Literal(null, IntegerType)
+  val nullString = Literal(null, StringType)
+  val testRelation = LocalRelation('a.string, 'b.string, 'c.string, 'd.string, 'e.int)
+
+  private def checkRewrite(rewrite: LogicalPlan): Unit = rewrite match {
+    case Aggregate(_, _, Aggregate(_, _, _: Expand)) =>
+    case _ => fail(s"Plan is not rewritten:\n$rewrite")
+  }
+
+  test("single distinct group") {
+    val input = testRelation
+      .groupBy('a)(countDistinct('e))
+      .analyze
+    val rewrite = RewriteDistinctAggregates(input)
+    comparePlans(input, rewrite)
+  }
+
+  test("single distinct group with partial aggregates") {
+    val input = testRelation
+      .groupBy('a, 'd)(
+        countDistinct('e, 'c).as('agg1),
+        max('b).as('agg2))
+      .analyze
+    val rewrite = RewriteDistinctAggregates(input)
+    comparePlans(input, rewrite)
+  }
+
+  test("single distinct group with non-partial aggregates") {
+    val input = testRelation
+      .groupBy('a, 'd)(
+        countDistinct('e, 'c).as('agg1),
+        CollectSet('b).toAggregateExpression().as('agg2))
+      .analyze
+    checkRewrite(RewriteDistinctAggregates(input))
+  }
+
+  test("multiple distinct groups") {
+    val input = testRelation
+      .groupBy('a)(countDistinct('b, 'c), countDistinct('d))
+      .analyze
+    checkRewrite(RewriteDistinctAggregates(input))
+  }
+
+  test("multiple distinct groups with partial aggregates") {
+    val input = testRelation
+      .groupBy('a)(countDistinct('b, 'c), countDistinct('d), sum('e))
+      .analyze
+    checkRewrite(RewriteDistinctAggregates(input))
+  }
+
+  test("multiple distinct groups with non-partial aggregates") {
+    val input = testRelation
+      .groupBy('a)(
+        countDistinct('b, 'c),
+        countDistinct('d),
+        CollectSet('b).toAggregateExpression())
+      .analyze
+    checkRewrite(RewriteDistinctAggregates(input))
+  }
+}
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/DataFrameAggregateSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/DataFrameAggregateSuite.scala
index 427390a90f..0e172bee4f 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/DataFrameAggregateSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/DataFrameAggregateSuite.scala
@@ -493,4 +493,12 @@ class DataFrameAggregateSuite extends QueryTest with SharedSQLContext {
         Row(new java.math.BigDecimal(2.0), new java.math.BigDecimal(1.5)),
         Row(new java.math.BigDecimal(3.0), new java.math.BigDecimal(1.5))))
   }
+
+  test("SPARK-17616: distinct aggregate combined with a non-partial aggregate") {
+    val df = Seq((1, 3, "a"), (1, 2, "b"), (3, 4, "c"), (3, 4, "c"), (3, 5, "d"))
+      .toDF("x", "y", "z")
+    checkAnswer(
+      df.groupBy($"x").agg(countDistinct($"y"), sort_array(collect_list($"z"))),
+      Seq(Row(1, 2, Seq("a", "b")), Row(3, 2, Seq("c", "c", "d"))))
+  }
 }