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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-6442) Extend TableAPI Support Sink Table Registration and ‘insert into’ Clause in SQL
Date Fri, 14 Jul 2017 17:12:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-6442?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16087607#comment-16087607
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ASF GitHub Bot commented on FLINK-6442:
---------------------------------------

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



> Extend TableAPI Support Sink Table Registration and ‘insert into’ Clause in SQL
> -------------------------------------------------------------------------------
>
>                 Key: FLINK-6442
>                 URL: https://issues.apache.org/jira/browse/FLINK-6442
>             Project: Flink
>          Issue Type: New Feature
>          Components: Table API & SQL
>            Reporter: lincoln.lee
>            Assignee: lincoln.lee
>            Priority: Minor
>
> Currently in TableAPI  there’s only registration method for source table,  when we
use SQL writing a streaming job, we should add additional part for the sink, like TableAPI
does:
> {code}
> val sqlQuery = "SELECT * FROM MyTable WHERE _1 = 3"
> val t = StreamTestData.getSmall3TupleDataStream(env)
> tEnv.registerDataStream("MyTable", t)
> // one way: invoke tableAPI’s writeToSink method directly
> val result = tEnv.sql(sqlQuery)
> result.writeToSink(new YourStreamSink)
> // another way: convert to datastream first and then invoke addSink 
> val result = tEnv.sql(sqlQuery).toDataStream[Row]
> result.addSink(new StreamITCase.StringSink)
> {code}
> From the api we can see the sink table always be a derived table because its 'schema'
is inferred from the result type of upstream query.
> Compare to traditional RDBMS which support DML syntax, a query with a target output could
be written like this:
> {code}
> insert into table target_table_name
> [(column_name [ ,...n ])]
> query
> {code}
> The equivalent form of the example above is as follows:
> {code}
>     tEnv.registerTableSink("targetTable", new YourSink)
>     val sql = "INSERT INTO targetTable SELECT a, b, c FROM sourceTable"
>     val result = tEnv.sql(sql)
> {code}
> It is supported by Calcite’s grammar: 
> {code}
>  insert:( INSERT | UPSERT ) INTO tablePrimary
>  [ '(' column [, column ]* ')' ]
>  query
> {code}
> I'd like to extend Flink TableAPI to support such feature.  see design doc: https://goo.gl/n3phK5



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