[GitHub] flink issue #3829: [FLINK-6442] [table] Extend TableAPI Support Sink Table R...

[lincoln-lil <gi...@git.apache.org>]

Github user lincoln-lil commented on the issue:

    https://github.com/apache/flink/pull/3829
  
    @fhueske, thanks for reviewing this. I read the design doc again, the original idea to support this functionality was doing minimal changes in the current state.  
    Yes, currently a TableSink's schema is always derived from the query result, and before it is configured the schema is null. Practically, I found that we can overwrite the getOutputType method to declare a concrete sink table's schema, and this can be used in a dml sql validation.
     So without adding an new SinkTable or modifying TableSink interface, we can choose keeping  writeToSink() method in TableAPI as a usage of derive table and tell users they can implement a custom type TableSink with output type declaration as a predefined schema.
    I'm not sure if we should add a new method like 'sqlInsert' for dml insert sql, and uncertain about the return type of an insert Operatoin in Flink(Calcite's TableModify defines output for DML(INSERT,DELETE,UPDATE) is a RowCount column of BigInt type). I'll discuss this with @shaoxuan-wang @wuchong and @sunjincheng121 offline.
    After that I'll update this PR according to your comments.
    Thanks, Lincoln



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