22/05/2022 22:28:33 自动保存草稿

[赢峰 <si...@163.com>]

在自定义表聚合函数 TableAggregateFunction 时使用的是 emitUpdateWithRetract 输出数据。在调用的时候参考文档的使用方式：
```
tEnv.from("stu_score")
    .groupBy($("course"))
    .flatAggregate(call(Top2RetractTableAggregateFunction.class, $("score")))
    .select($("course"), $("f0"), $("f1"))
```
使用默认 blink Planner，会抛出如下异常：
```
Exception in thread "main" org.apache.flink.table.api.ValidationException: Could not find an implementation method 'emitValue' in class 'com.flink.example.table.function.custom.Top2RetractTableAggregateFunction' for function 'Top2' that matches the following signature:
void emitValue(com.flink.example.table.function.custom.Top2RetractTableAggregateFunction.Top2RetractAccumulator, org.apache.flink.util.Collector)
```
但是使用 Old Planner，则会正常输出：
```
StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
env.setParallelism(1);
EnvironmentSettings settings = EnvironmentSettings
        .newInstance()
        .useOldPlanner()
        .inStreamingMode()
        .build();
StreamTableEnvironment tEnv = StreamTableEnvironment.create(env, settings);
```
这是什么地方使用有问题？