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Posted to issues@spark.apache.org by "Sunitha Kambhampati (JIRA)" <ji...@apache.org> on 2018/08/01 18:43:00 UTC
[jira] [Commented] (SPARK-19602) Unable to query using the fully
qualified column name of the form ( ..)
[ https://issues.apache.org/jira/browse/SPARK-19602?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16565802#comment-16565802 ]
Sunitha Kambhampati commented on SPARK-19602:
---------------------------------------------
The design doc is also uploaded [here|https://drive.google.com/file/d/1zKm3aNZ3DpsqIuoMvRsf0kkDkXsAasxH/view]
> Unable to query using the fully qualified column name of the form ( <DBNAME>.<TABLENAME>.<COLUMNNAME>)
> ------------------------------------------------------------------------------------------------------
>
> Key: SPARK-19602
> URL: https://issues.apache.org/jira/browse/SPARK-19602
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.1.0
> Reporter: Sunitha Kambhampati
> Assignee: Sunitha Kambhampati
> Priority: Major
> Attachments: Design_ColResolution_JIRA19602.pdf
>
>
> 1) Spark SQL fails to analyze this query: select db1.t1.i1 from db1.t1, db2.t1
> Most of the other database systems support this ( e.g DB2, Oracle, MySQL).
> Note: In DB2, Oracle, the notion is of <schema>.<tablename>.<columnname>
> 2) Another scenario where this fully qualified name is useful is as follows:
> // current database is db1.
> select t1.i1 from t1, db2.t1
> If the i1 column exists in both tables: db1.t1 and db2.t1, this will throw an error during column resolution in the analyzer, as it is ambiguous.
> Lets say the user intended to retrieve i1 from db1.t1 but in the example db2.t1 only has i1 column. The query would still succeed instead of throwing an error.
> One way to avoid confusion would be to explicitly specify using the fully qualified name db1.t1.i1
> For e.g: select db1.t1.i1 from t1, db2.t1
> Workarounds:
> There is a workaround for these issues, which is to use an alias.
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