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https://issues.apache.org/jira/browse/FLINK-3097?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15383717#comment-15383717
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ASF GitHub Bot commented on FLINK-3097:
---------------------------------------
Github user twalthr commented on the issue:
https://github.com/apache/flink/pull/2265
No, there is no FLIP about it. I think a discussion in JIRA or in this PR
should be enough. That's why I haven't documented it yet. I was inspired by
your
[document](https://docs.google.com/document/d/1KMUzvBAWSyQ39T8MyxUi0zNHyvLUnyGMPA7_RLSDpFw/edit).
You are right, `ScalarFunction` has many internal functions but they are not
exposed to the user, only 2 methods can be overriden.
An interface is not enough as it might be sometimes necessary to override
`getReturnType` and `getParameterType`.
> Add support for custom functions in Table API
> ---------------------------------------------
>
> Key: FLINK-3097
> URL: https://issues.apache.org/jira/browse/FLINK-3097
> Project: Flink
> Issue Type: New Feature
> Components: Table API & SQL
> Reporter: Timo Walther
> Assignee: Timo Walther
>
> Currently, the Table API has a very limited set of built-in functions.
> Support for custom functions can solve this problem. Adding of a custom row
> function could look like:
> {code}
> TableEnvironment tableEnv = new TableEnvironment();
> RowFunction<String> rf = new RowFunction<String>() {
> @Override
> public String call(Object[] args) {
> return ((String) args[0]).trim();
> }
> };
> tableEnv.getConfig().registerRowFunction("TRIM", rf,
> BasicTypeInfo.STRING_TYPE_INFO);
> DataSource<Tuple1<String>> input = env.fromElements(
> new Tuple1<>(" 1 "));
> Table table = tableEnv.fromDataSet(input);
> Table result = table.select("TRIM(f0)");
> {code}
> This feature is also necessary as part of FLINK-2099.
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