[SPARK-24369][SQL] Correct handling for multiple distinct aggregations having the same argument set

## What changes were proposed in this pull request?
This pr fixed an issue when having multiple distinct aggregations having the same argument set, e.g.,
```
scala>: paste
val df = sql(
  s"""SELECT corr(DISTINCT x, y), corr(DISTINCT y, x), count(*)
     | FROM (VALUES (1, 1), (2, 2), (2, 2)) t(x, y)
   """.stripMargin)

java.lang.RuntimeException
You hit a query analyzer bug. Please report your query to Spark user mailing list.
```
The root cause is that `RewriteDistinctAggregates` can't detect multiple distinct aggregations if they have the same argument set. This pr modified code so that `RewriteDistinctAggregates` could count the number of aggregate expressions with `isDistinct=true`.

## How was this patch tested?
Added tests in `DataFrameAggregateSuite`.

Author: Takeshi Yamamuro <[email protected]>

Closes #21443 from maropu/SPARK-24369.

Author: maropu

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/RewriteDistinctAggregates.scala

@@ -115,7 +115,8 @@ object RewriteDistinctAggregates extends Rule[LogicalPlan] {
     }
 
     // Extract distinct aggregate expressions.
-    val distinctAggGroups = aggExpressions.filter(_.isDistinct).groupBy { e =>
+    val distincgAggExpressions = aggExpressions.filter(_.isDistinct)
+    val distinctAggGroups = distincgAggExpressions.groupBy { e =>
         val unfoldableChildren = e.aggregateFunction.children.filter(!_.foldable).toSet
         if (unfoldableChildren.nonEmpty) {
           // Only expand the unfoldable children
@@ -132,7 +133,7 @@ object RewriteDistinctAggregates extends Rule[LogicalPlan] {
     }
 
     // Aggregation strategy can handle queries with a single distinct group.
-    if (distinctAggGroups.size > 1) {
+    if (distincgAggExpressions.size > 1) {
       // Create the attributes for the grouping id and the group by clause.
       val gid = AttributeReference("gid", IntegerType, nullable = false)()
       val groupByMap = a.groupingExpressions.collect {
@@ -151,7 +152,7 @@ object RewriteDistinctAggregates extends Rule[LogicalPlan] {
       }
 
       // Setup unique distinct aggregate children.
-      val distinctAggChildren = distinctAggGroups.keySet.flatten.toSeq.distinct
+      val distinctAggChildren = distinctAggGroups.keySet.flatten.toSeq
       val distinctAggChildAttrMap = distinctAggChildren.map(expressionAttributePair)
       val distinctAggChildAttrs = distinctAggChildAttrMap.map(_._2)
 

sql/core/src/main/scala/org/apache/spark/sql/execution/SparkStrategies.scala

@@ -386,7 +386,7 @@ abstract class SparkStrategies extends QueryPlanner[SparkPlan] {
           aggregateExpressions.partition(_.isDistinct)
         if (functionsWithDistinct.map(_.aggregateFunction.children).distinct.length > 1) {
           // This is a sanity check. We should not reach here when we have multiple distinct
-          // column sets. Our MultipleDistinctRewriter should take care this case.
+          // column sets. Our `RewriteDistinctAggregates` should take care this case.
           sys.error("You hit a query analyzer bug. Please report your query to " +
               "Spark user mailing list.")
         }

sql/core/src/test/resources/sql-tests/inputs/group-by.sql

@@ -68,4 +68,8 @@ SELECT 1 from (
   FROM (select 1 as x) a
   WHERE false
 ) b
-where b.z != b.z
+where b.z != b.z;
+
+-- SPARK-24369 multiple distinct aggregations having the same argument set
+SELECT corr(DISTINCT x, y), corr(DISTINCT y, x), count(*)
+  FROM (VALUES (1, 1), (2, 2), (2, 2)) t(x, y);

sql/core/src/test/resources/sql-tests/results/group-by.sql.out

@@ -1,5 +1,5 @@
 -- Automatically generated by SQLQueryTestSuite
--- Number of queries: 26
+-- Number of queries: 27
 
 
 -- !query 0
@@ -241,3 +241,12 @@ where b.z != b.z
 struct<1:int>
 -- !query 25 output
 
+
+
+-- !query 26
+SELECT corr(DISTINCT x, y), corr(DISTINCT y, x), count(*)
+  FROM (VALUES (1, 1), (2, 2), (2, 2)) t(x, y)
+-- !query 26 schema
+struct<corr(DISTINCT CAST(x AS DOUBLE), CAST(y AS DOUBLE)):double,corr(DISTINCT CAST(y AS DOUBLE), CAST(x AS DOUBLE)):double,count(1):bigint>
+-- !query 26 output
+1.0	1.0	3