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https://issues.apache.org/jira/browse/BEAM-6133?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on BEAM-6133 started by Gleb Kanterov.
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> [SQL] Add support for TableMacro UDF
> ------------------------------------
>
>                 Key: BEAM-6133
>                 URL: https://issues.apache.org/jira/browse/BEAM-6133
>             Project: Beam
>          Issue Type: New Feature
>          Components: dsl-sql
>            Reporter: Gleb Kanterov
>            Assignee: Gleb Kanterov
>            Priority: Major
>          Time Spent: 2h 20m
>  Remaining Estimate: 0h
>
> Now we support only ScalarFunction UDFs. In Calcite, there are other kinds of 
> UDFs. With TableMacro UDFs users can connect external data sources in a 
> similar way as in TableProvider, but without specifying a schema, or 
> enumerating a list of existing tables in advance. 
> An example use case is connecting external metadata service and querying 
> range of partitions.
> {code}
> SELECT COUNT(*) FROM table(my_udf('dataset', start = '2017-01-01', end = 
> '2018-01-01'))
> {code}
> Where the implementation of `my_udf` will connect to this service, get file 
> locations for a range of partitions, and translate to PTransform reading it.



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