sigmod commented on code in PR #36117:
URL: https://github.com/apache/spark/pull/36117#discussion_r848067621
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala:
##########
@@ -411,14 +412,26 @@ abstract class Optimizer(catalogManager: CatalogManager)
}
/**
- * Remove useless DISTINCT for MAX and MIN.
+ * Remove useless DISTINCT:
+ * 1. For some aggregate expression, e.g.: MAX and MIN.
+ * 2. If the distinct semantics is guaranteed by child.
+ *
* This rule should be applied before RewriteDistinctAggregates.
*/
object EliminateDistinct extends Rule[LogicalPlan] {
- override def apply(plan: LogicalPlan): LogicalPlan =
plan.transformAllExpressionsWithPruning(
- _.containsPattern(AGGREGATE_EXPRESSION)) {
- case ae: AggregateExpression if ae.isDistinct &&
isDuplicateAgnostic(ae.aggregateFunction) =>
- ae.copy(isDistinct = false)
+ override def apply(plan: LogicalPlan): LogicalPlan =
plan.transformWithPruning(
+ _.containsPattern(AGGREGATE)) {
+ case agg: Aggregate =>
+
agg.transformExpressionsWithPruning(_.containsPattern(AGGREGATE_EXPRESSION)) {
+ case ae: AggregateExpression if ae.isDistinct &&
+ isDuplicateAgnostic(ae.aggregateFunction) =>
+ ae.copy(isDistinct = false)
+
+ case ae: AggregateExpression if ae.isDistinct &&
+ agg.child.distinctKeys.exists(
+
_.subsetOf(ExpressionSet(ae.aggregateFunction.children.filterNot(_.foldable))))
=>
Review Comment:
Is it correct?
If input plan to this rule is:
```
SELECT a, count(distinct c) FROM (
SELECT distinct a, b, c
FROM t
)
GROUP BY a
```
Will the added case branch rewrite the plan to
```
SELECT a, count(c) FROM (
SELECT distinct a, b, c
FROM t
)
GROUP BY a
```
agg.child.distinctKeys is `{a, b, c}`
ExpressionSet(ae.aggregateFunction.children.filterNot(_.foldable)) is `{c}`.
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