Kurt Young commented on FLINK-5185:

Hi [~fhueske], you are right about the schema thing. It's indeed decided by 
RelOptRule and TableSource together. 

Regarding to the simplify part, i think it's almost the same with these two 
approaches. Like we metioned in the design doc, we will have a projectable 
source which will extends TableSource and with ProjectableTableSource trait. 
Once the projection been pushdown, the change of schema will reflected through 
TableSource's interface {{getFieldTypes}}, which is sufficient for us to 
derived the changed RowType. 

We will open some PRs soon and let's discuss with the codes. 

> Decouple BatchTableSourceScan with TableSourceTable
> ---------------------------------------------------
>                 Key: FLINK-5185
>                 URL: https://issues.apache.org/jira/browse/FLINK-5185
>             Project: Flink
>          Issue Type: Improvement
>          Components: Table API & SQL
>    Affects Versions: 1.2.0
>            Reporter: Kurt Young
>            Assignee: zhangjing
>            Priority: Minor
> As the components' relationship show in this design doc:
> https://docs.google.com/document/d/1PBnEbOcFHlEF1qGGAUgJvINdEXzzFTIRElgvs4-Tdeo/
> We found it's been annoying for {{BatchTableSourceScan}} directly holding 
> {{TableSourceTable}}, and refer to {{TableSource}} further. It's ok if the 
> relationship is immutable, but when we want to change the {{TableSource}} 
> when applying optimizations, it will cause some conflicts and 
> misunderstanding. 
> Since there is only one way to change {{TableSource}}, which is creating a 
> new {{TableSourceTable}} to hold the new {{TableSource}}, and create a new 
> {{BatchTableSourceScan}} pointing to the {{TableSourceTable}} which just 
> created. The annoying part is the {{RelOptTable}} comes from the super class 
> {{TableScan}} still holds the connection to the original {{TableSourceTable}} 
> and {{TableSource}}. It will cause some misunderstanding, which one should 
> the {{Scan}} rely to, and what's difference between these tables. 
> Besides, {{TableSourceTable}} is not very useful in {{BatchTableSourceScan}}, 
> the only thing {{Scan}} cares is the {{RowType}} it returns, since this is 
> and should be decided by {{TableSource}}. So we can let 
> {{BatchTableSourceScan}} directly holding {{TableSource}} instead of holding 
> {{TableSourceTable}}.If some original information are needed, find table 
> through {{RelOptTable}}. 

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