Unknown call expression: avg(amount)－官方文档示例补全后报错(含:完整代码＋异常栈＋文档出处)，谢谢

[Appleyuchi]

来自文档:
https://ci.apache.org/projects/flink/flink-docs-release-1.11/dev/table/tableApi.html
的Distinct aggregation on over window


代码:
https://paste.ubuntu.com/p/q97Rg4zDHS/


异常栈:
Exception in thread "main" java.lang.RuntimeException: Unknown call expression: avg(amount)
at org.apache.flink.table.planner.expressions.converter.ExpressionConverter.visit(ExpressionConverter.java:102)
at org.apache.flink.table.planner.expressions.converter.ExpressionConverter.visit(ExpressionConverter.java:72)
at org.apache.flink.table.expressions.CallExpression.accept(CallExpression.java:122)
at org.apache.flink.table.planner.expressions.converter.ExpressionConverter$1.toRexNode(ExpressionConverter.java:226)
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1374)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
at org.apache.flink.table.planner.expressions.converter.OverConvertRule.convert(OverConvertRule.java:81)
at org.apache.flink.table.planner.expressions.converter.ExpressionConverter.visit(ExpressionConverter.java:97)
at org.apache.flink.table.planner.expressions.converter.ExpressionConverter.visit(ExpressionConverter.java:72)
at org.apache.flink.table.expressions.CallExpression.accept(CallExpression.java:122)
at org.apache.flink.table.planner.expressions.converter.ExpressionConverter$1.toRexNode(ExpressionConverter.java:226)
at org.apache.flink.table.planner.expressions.converter.CustomizedConvertRule.convertAs(CustomizedConvertRule.java:275)
at org.apache.flink.table.planner.expressions.converter.CustomizedConvertRule.lambda$convert$0(CustomizedConvertRule.java:95)
at java.util.Optional.map(Optional.java:215)
at org.apache.flink.table.planner.expressions.converter.CustomizedConvertRule.convert(CustomizedConvertRule.java:95)
at org.apache.flink.table.planner.expressions.converter.ExpressionConverter.visit(ExpressionConverter.java:97)
at org.apache.flink.table.planner.expressions.converter.ExpressionConverter.visit(ExpressionConverter.java:72)
at org.apache.flink.table.expressions.CallExpression.accept(CallExpression.java:122)
at org.apache.flink.table.planner.plan.QueryOperationConverter.convertExprToRexNode(QueryOperationConverter.java:741)
at org.apache.flink.table.planner.plan.QueryOperationConverter.access$800(QueryOperationConverter.java:132)
at org.apache.flink.table.planner.plan.QueryOperationConverter$SingleRelVisitor.lambda$convertToRexNodes$6(QueryOperationConverter.java:547)
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1374)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
at org.apache.flink.table.planner.plan.QueryOperationConverter$SingleRelVisitor.convertToRexNodes(QueryOperationConverter.java:548)
at org.apache.flink.table.planner.plan.QueryOperationConverter$SingleRelVisitor.visit(QueryOperationConverter.java:156)
at org.apache.flink.table.planner.plan.QueryOperationConverter$SingleRelVisitor.visit(QueryOperationConverter.java:152)
at org.apache.flink.table.operations.ProjectQueryOperation.accept(ProjectQueryOperation.java:75)
at org.apache.flink.table.planner.plan.QueryOperationConverter.defaultMethod(QueryOperationConverter.java:149)
at org.apache.flink.table.planner.plan.QueryOperationConverter.defaultMethod(QueryOperationConverter.java:131)
at org.apache.flink.table.operations.utils.QueryOperationDefaultVisitor.visit(QueryOperationDefaultVisitor.java:47)
at org.apache.flink.table.operations.ProjectQueryOperation.accept(ProjectQueryOperation.java:75)
at org.apache.flink.table.planner.calcite.FlinkRelBuilder.queryOperation(FlinkRelBuilder.scala:165)
at org.apache.flink.table.planner.delegation.PlannerBase.translateToRel(PlannerBase.scala:247)
at org.apache.flink.table.planner.delegation.PlannerBase.$anonfun$translate$1(PlannerBase.scala:163)
at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:233)
at scala.collection.Iterator.foreach(Iterator.scala:937)
at scala.collection.Iterator.foreach$(Iterator.scala:937)
at scala.collection.AbstractIterator.foreach(Iterator.scala:1425)
at scala.collection.IterableLike.foreach(IterableLike.scala:70)
at scala.collection.IterableLike.foreach$(IterableLike.scala:69)
at scala.collection.AbstractIterable.foreach(Iterable.scala:54)
at scala.collection.TraversableLike.map(TraversableLike.scala:233)
at scala.collection.TraversableLike.map$(TraversableLike.scala:226)
at scala.collection.AbstractTraversable.map(Traversable.scala:104)
at org.apache.flink.table.planner.delegation.PlannerBase.translate(PlannerBase.scala:163)
at org.apache.flink.table.api.bridge.java.internal.StreamTableEnvironmentImpl.toDataStream(StreamTableEnvironmentImpl.java:331)
at org.apache.flink.table.api.bridge.java.internal.StreamTableEnvironmentImpl.toRetractStream(StreamTableEnvironmentImpl.java:307)
at org.apache.flink.table.api.bridge.java.internal.StreamTableEnvironmentImpl.toRetractStream(StreamTableEnvironmentImpl.java:298)
at DistinctAggregation3.main(DistinctAggregation3.java:74)
问题:
①avg().distinct()不是代表取平均后进行去重吗？
取平均后不是只有一个数了吗为啥还需要去重？
②代码如何修改？才能run起来?


谢谢各位大佬～