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https://issues.apache.org/jira/browse/DRILL-5550?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16927653#comment-16927653
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ASF GitHub Bot commented on DRILL-5550:
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arina-ielchiieva commented on issue #939: DRILL-5550: Missing CSV column value
set to null
URL: https://github.com/apache/drill/pull/939#issuecomment-530428270
Closing PR since it's no longer valid to to new text reader introduction.
Keeping the Jira open though since issue still persists.
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> SELECT non-existent column produces empty required VARCHAR
> ----------------------------------------------------------
>
> Key: DRILL-5550
> URL: https://issues.apache.org/jira/browse/DRILL-5550
> Project: Apache Drill
> Issue Type: Bug
> Components: Storage - Text & CSV
> Affects Versions: 1.10.0
> Reporter: Paul Rogers
> Priority: Minor
> Fix For: Future
>
>
> Drill's CSV column reader supports two forms of files:
> * Files with column headers as the first line of the file.
> * Files without column headers.
> The CSV storage plugin specifies which format to use for files accessed via
> that storage plugin config.
> Suppose we have a CSV file with headers:
> {code}
> a,b,c
> 10,foo,bar
> {code}
> Suppose we configure a storage plugin to use headers:
> {code}
> TextFormatConfig csvFormat = new TextFormatConfig();
> csvFormat.fieldDelimiter = ',';
> csvFormat.skipFirstLine = false;
> csvFormat.extractHeader = true;
> {code}
> (The above can also be done using JSON when running Drill as a server.)
> Execute the following query:
> {code}
> SELECT a, c, d FROM `dfs.data.example.csv`
> {code}
> Results:
> {code}
> a,c,d
> 10,bar,
> {code}
> The actual type of column {{d}} is non-nullable VARCHAR.
> This is inconsistent with other parts of Drill in two ways, one may be a bug.
> Most other parts of Drill use a nullable INT for "missing" columns.
> 1. For CSV it makes sense for the data type to be VARCHAR, since all CSV
> columns are of that type.
> 2. It may *not* make sense for the column to be non-nullable and blank rather
> than nullable and NULL. In SQL, NULL means that the data is unknown, which is
> the case here.
> In the future, we may want to use some other indication for a missing column.
> Until then, the requested change is to make the type of a missing CSV column
> a nullable VARCHAR set to value NULL.
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