Re: Reverse the order of fields in Flink SQL

[yinhua.dai]

Hi Timo,

I write simple testing code for the issue, please checkout
https://gist.github.com/yinhua-dai/143304464270afd19b6a926531f9acb1

I write a custom table source which just use RowCsvInputformat to create the
dataset, and use the provided CsvTableSink, and can reproduce the issue.



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Re: Reverse the order of fields in Flink SQL

[yinhua.dai]

I think I have already done that in my custom sink.

 @Override
  public String[] getFieldNames() {
return this.fieldNames;
  }

  @Override
  public TypeInformation[] getFieldTypes() {

return this.fieldTypes;
  }

@Override
  public TableSink configure(String[] fieldNames, TypeInformation[]
fieldTypes) {
this.fieldNames = fieldNames;
this.fieldTypes = fieldTypes;
return this;
  }



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Re: Reverse the order of fields in Flink SQL

[Timo Walther]

Hi Yinhua,

your custom sink must implement 
`org.apache.flink.table.sinks.TableSink#configure`. This method is 
called when writing to a sink such that the sink can configure itself 
for the reverse order. The methods `getFieldTypes` and `getFieldNames` 
must then return the reconfigured schema; must match to the query result 
schema.


Regards,
Timo


Am 23.10.18 um 09:47 schrieb yinhua.dai:

I write a customized table source, and it emits some fields let's say f1, f2.

And then I just write to a sink with a reversed order of fields, as below:
*select f2, f1 from customTableSource*

And I found that it actually doesn't do the field reverse.


Then I tried with flink provided CsvTableSource and CsvTableSink, I found
that it has no problem reverse the order, and after some investigation I
found that it's related with two things:
1. *CsvTableSource* implemented *ProjectableTableSource*
2. *RowCsvInputFormat* supports *selectedFields*

Do I have to do the two things as well in my custom table source to get the
reverse work?



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Reverse the order of fields in Flink SQL

[yinhua.dai]

I write a customized table source, and it emits some fields let's say f1, f2.

And then I just write to a sink with a reversed order of fields, as below:
*select f2, f1 from customTableSource*

And I found that it actually doesn't do the field reverse.


Then I tried with flink provided CsvTableSource and CsvTableSink, I found
that it has no problem reverse the order, and after some investigation I
found that it's related with two things:
1. *CsvTableSource* implemented *ProjectableTableSource*
2. *RowCsvInputFormat* supports *selectedFields*

Do I have to do the two things as well in my custom table source to get the
reverse work?



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