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https://issues.apache.org/jira/browse/DRILL-2849?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14508115#comment-14508115
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Venki Korukanti commented on DRILL-2849:
----------------------------------------
CSV writer creates a header row from the column names. Is that why you are
seeing an extra row? Can you open the output file and check?
> Difference in query results over CSV file created by CTAS, compared to
> results over original CSV file
> ------------------------------------------------------------------------------------------------------
>
> Key: DRILL-2849
> URL: https://issues.apache.org/jira/browse/DRILL-2849
> Project: Apache Drill
> Issue Type: Bug
> Components: Storage - Text & CSV
> Affects Versions: 0.9.0
> Environment: 64e3ec52b93e9331aa5179e040eca19afece8317 | DRILL-2611:
> value vectors should report valid value count | 16.04.2015 @ 13:53:34 EDT
> Reporter: Khurram Faraaz
> Assignee: Steven Phillips
> Priority: Critical
>
> Different results are seen for the same query over CSV data file and another
> CSV data file created by CTAS using the same CSV file.
> Tests were executed on 4 node cluster on CentOS.
> I got rid of the header information that is written by CTAS into the new CSV
> file that CTAS creates, and then ran my queries over CTAS' CSV file.
> query over uncompressed CSV file, deletions/deletions-00000-of-00020.csv
> {code}
> > select count(cast(columns[0] as double)),max(cast(columns[0] as
> > double)),min(cast(columns[0] as double)),avg(cast(columns[0] as double)),
> > columns[7] from `deletions/deletions-00000-of-00020.csv` group by
> > columns[7];
> 88 rows selected (6.893 seconds)
> =================================================
> {code}
> query over CSV file that was created by CTAS. (input to CTAS was
> deletions/deletions-00000-of-00020.csv)
> Notice there is one more record returned.
> {code}
> > select count(cast(columns[0] as double)),max(cast(columns[0] as
> > double)),min(cast(columns[0] as double)),avg(cast(columns[0] as double)),
> > columns[7] from `csvToCSV_00000_of_00020/0_0_0.csv` group by columns[7];
>
> 89 rows selected (6.623 seconds)
> ==================================================
> {code}
> query over compressed CSV file
> {code}
> > select count(cast(columns[0] as double)),max(cast(columns[0] as
> > double)),min(cast(columns[0] as double)),avg(cast(columns[0] as double)),
> > columns[7] from `deletions-00000-of-00020.csv.gz` group by columns[7];
> 88 rows selected (10.526 seconds)
> ==================================================
> {code}
> In the below cases, the count and sum results are different when query is
> executed over CSV file that was created by CTAS. ( this may explain why we
> see the difference in results in the above queries ? )
> {code}
> 0: jdbc:drill:> select count(cast(columns[0] as double)),max(cast(columns[0]
> as double)),min(cast(columns[0] as double)),avg(cast(columns[0] as double)),
> columns[7] from `deletions/deletions-00000-of-00020.csv` where columns[7] is
> null group by columns[7];
> +------------+------------+------------+------------+------------+
> | EXPR$0 | EXPR$1 | EXPR$2 | EXPR$3 | EXPR$4 |
> +------------+------------+------------+------------+------------+
> | 252 | 1.362983396001E12 | 1.165768779027E12 | 1.293794515595635E12 |
> null |
> +------------+------------+------------+------------+------------+
> 1 row selected (6.013 seconds)
> 0: jdbc:drill:> select count(cast(columns[0] as double)),max(cast(columns[0]
> as double)),min(cast(columns[0] as double)),avg(cast(columns[0] as double)),
> columns[7] from `deletions-00000-of-00020.csv.gz` where columns[7] is null
> group by columns[7];
> +------------+------------+------------+------------+------------+
> | EXPR$0 | EXPR$1 | EXPR$2 | EXPR$3 | EXPR$4 |
> +------------+------------+------------+------------+------------+
> | 252 | 1.362983396001E12 | 1.165768779027E12 | 1.293794515595635E12 |
> null |
> +------------+------------+------------+------------+------------+
> 1 row selected (8.899 seconds)
> {code}
> Notice that count and sum results are different (from those above) when query
> is executed over the CSV file created by CTAS.
> {code}
> 0: jdbc:drill:> select count(cast(columns[0] as double)),max(cast(columns[0]
> as double)),min(cast(columns[0] as double)),avg(cast(columns[0] as double)),
> columns[7] from `csvToCSV_00000_of_00020/0_0_0.csv` where columns[7] is null
> group by columns[7];
> +------------+------------+------------+------------+------------+
> | EXPR$0 | EXPR$1 | EXPR$2 | EXPR$3 | EXPR$4 |
> +------------+------------+------------+------------+------------+
> | 245 | 1.349670663E12 | 1.165768779027E12 | 1.2930281335065144E12 |
> null |
> +------------+------------+------------+------------+------------+
> 1 row selected (5.736 seconds)
> {code}
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