JingGe commented on code in PR #23796:
URL: https://github.com/apache/flink/pull/23796#discussion_r1404850835
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docs/content.zh/docs/dev/table/functions/udfs.md:
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@@ -1797,7 +1797,7 @@ public static class Top2 extends
TableAggregateFunction<Tuple2<Integer, Integer>
// 注册函数
StreamTableEnvironment tEnv = ...
-tEnv.registerFunction("top2", new Top2());
+tEnv.createTemporarySystemFunction("top2", new Top2());
Review Comment:
ditto.
It is recommended to use class over new instance for udf that can be
instanced with no parameter, because Flink as the framework can add more logic
to control the process of creating new instance underneath, e.g. validation
which is the built-in standard logic in TableEnvironmentImpl. More logic or
optimization could be added in the future with no impact on users' existing
code.
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