[GitHub] [spark] beliefer commented on a change in pull request #29291: [SPARK-30276][SQL] Support Filter expression allows simultaneous use of DISTINCT

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beliefer commented on a change in pull request #29291:
URL: https://github.com/apache/spark/pull/29291#discussion_r462924626



##########
File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/RewriteDistinctAggregates.scala
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@@ -144,28 +192,23 @@ import org.apache.spark.sql.types.IntegerType
  */
 object RewriteDistinctAggregates extends Rule[LogicalPlan] {
 
-  private def mayNeedtoRewrite(exprs: Seq[Expression]): Boolean = {
-    val distinctAggs = exprs.flatMap { _.collect {
-      case ae: AggregateExpression if ae.isDistinct => ae
-    }}
-    // We need at least two distinct aggregates for this rule because aggregation
-    // strategy can handle a single distinct group.
+  private def mayNeedtoRewrite(a: Aggregate): Boolean = {
+    val aggExpressions = collectAggregateExprs(a)
+    val distinctAggs = aggExpressions.filter(_.isDistinct)
+    // We need at least two distinct aggregates or the single distinct aggregate group exists filter
+    // clause for this rule because aggregation strategy can handle a single distinct aggregate
+    // group without filter clause.
     // This check can produce false-positives, e.g., SUM(DISTINCT a) & COUNT(DISTINCT a).
-    distinctAggs.size > 1
+    distinctAggs.size > 1 || (distinctAggs.size == 1 && aggExpressions.exists(_.filter.isDefined))

Review comment:
       If `distinctAggs.size == 0` and `aggExpressions.exists(_.filter.isDefined)`,  we not need this rewrite.




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