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https://issues.apache.org/jira/browse/FLINK-30292?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17648563#comment-17648563
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Timo Walther commented on FLINK-30292:
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Thanks for starting this discussion [~yunfengzhou]. I agree that the current
approach using `ExternalTypeInfo` adds some serialization overhead. It was
introduced to eliminate any friction during conversion of both type systems
during conversion Table API->DataStream API. This purpose was successful.
However, we can further evolve `ExternalTypeInfo` and use more specialized type
info/serializers. In theory, if the `DataType` is of class `Row` with default
conversions in every subfield, `ExternalTypeInfo.of` can also return
`RowTypeInfo` with `BasicTypeInfo.*` etc. This specialized logic has just not
been implemented yet.
In any case, there were already discussion about introducing a dedicated
`table-types` module to ease the development and expose common utilities
including the data structure converters.
> Better support for conversion between DataType and TypeInformation
> ------------------------------------------------------------------
>
> Key: FLINK-30292
> URL: https://issues.apache.org/jira/browse/FLINK-30292
> Project: Flink
> Issue Type: Improvement
> Components: Table SQL / API
> Affects Versions: 1.15.3
> Reporter: Yunfeng Zhou
> Priority: Major
>
> In Flink 1.15, we have the following ways to convert a DataType to a
> TypeInformation. Each of them has some disadvantages.
> * `TypeConversions.fromDataTypeToLegacyInfo`
> It might lead to precision losses in face of some data types like timestamp.
> It has been deprecated.
> * `ExternalTypeInfo.of`
> It cannot be used to get detailed type information like `RowTypeInfo`
> It might bring some serialization overhead.
> Given that the ways mentioned above are both not perfect, Flink SQL should
> provide a better API to support DataType-TypeInformation conversions, and
> thus better support Table-DataStream conversions.
>
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