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https://issues.apache.org/jira/browse/FLINK-7548?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16209299#comment-16209299
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Fabian Hueske commented on FLINK-7548:
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Thanks for the comment [~ykt836].
I think the projection push-down behavior is similar as before. When a
projection is pushed down, a {{TableSource}} is not modified but we create a
new {{TableSource}} with reduced schema. This is what happens at the moment as
well. The difference is that right now the schema is inferred by the Table API
/ SQL internals from the return type and with my change the schema would be
explicitly given by the {{TableSource}}. This makes it easier to support
projection push-down also for {{TableSource}} implementations with time fields
because these would no longer be automatically merged into the schema by the
Table API internals but instead the {{TableSource}} knows everything about its
schema.
Nonetheless, you are right. When projections are pushed down, a {{TableSource}}
needs generate a new return type and new schema for the new {{TableSource}}
(and possibly adjust the rowtime / proctime field information).
> Support watermark generation for TableSource
> --------------------------------------------
>
> Key: FLINK-7548
> URL: https://issues.apache.org/jira/browse/FLINK-7548
> Project: Flink
> Issue Type: Improvement
> Components: Table API & SQL
> Reporter: Jark Wu
> Assignee: Fabian Hueske
> Priority: Blocker
> Fix For: 1.4.0
>
>
> As discussed in FLINK-7446, currently the TableSource only support to define
> rowtime field, but not support to extract watermarks from the rowtime field.
> We can provide a new interface called {{DefinedWatermark}}, which has two
> methods {{getRowtimeAttribute}} (can only be an existing field) and
> {{getWatermarkGenerator}}. The {{DefinedRowtimeAttribute}} will be marked
> deprecated.
> How to support periodic and punctuated watermarks and support some built-in
> strategies needs further discussion.
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