[jira] [Comment Edited] (AIRFLOW-2254) Fix header output on RedshiftToS3Transfer

["Sathyaprakash Govindasamy (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AIRFLOW-2254?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16421607#comment-16421607 ] 

Sathyaprakash Govindasamy edited comment on AIRFLOW-2254 at 4/1/18 8:40 AM:
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Pull request created to fix the issue where header row is not coming as first when data type of first column is not a number but varchar

[https://github.com/apache/incubator-airflow/pull/3180]


was (Author: sathyaprakashg):
Pull request created to fix the issue where header row is not coming as first when data type of first column is not integer

https://github.com/apache/incubator-airflow/pull/3180

> Fix header output on RedshiftToS3Transfer
> -----------------------------------------
>
>                 Key: AIRFLOW-2254
>                 URL: https://issues.apache.org/jira/browse/AIRFLOW-2254
>             Project: Apache Airflow
>          Issue Type: Bug
>          Components: aws, redshift
>            Reporter: Kengo Seki
>            Assignee: Sathyaprakash Govindasamy
>            Priority: Major
>
> The current implementation of RedshiftToS3Transfer is as follows and seems to have referred to [this post|https://medium.com/carwow-product-engineering/unloading-a-file-from-redshift-to-s3-with-headers-fb707f5480f7].
> {code}
>         unload_query = """
>                         UNLOAD ('SELECT {0}
>                         UNION ALL
>                         SELECT {1} FROM {2}.{3}
>                         ORDER BY 1 DESC')
>                         TO 's3://{4}/{5}/{3}_'
>                         with
>                         credentials 'aws_access_key_id={6};aws_secret_access_key={7}'
>                         {8};
>                         """.format(column_names, column_castings, self.schema, self.table,
>                                    self.s3_bucket, self.s3_key, credentials.access_key,
>                                    credentials.secret_key, unload_options)
> {code}
> {{ORDER BY 1 DESC}} is intended to output the header first, but as [this post|https://stackoverflow.com/questions/24681214/unloading-from-redshift-to-s3-with-headers#answer-26443374] says, it works only if the first column type is not character (e.g. numeric).
> In addition, this query should be used with PARALLEL OFF option, because without that, many files are output but only the first one has the header line.



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