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Posted to issues@spark.apache.org by "Apache Spark (JIRA)" <ji...@apache.org> on 2016/07/17 16:57:20 UTC
[jira] [Assigned] (SPARK-16594) Physical Plan Differences when
Table Scan Having Duplicate Columns
[ https://issues.apache.org/jira/browse/SPARK-16594?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Apache Spark reassigned SPARK-16594:
------------------------------------
Assignee: (was: Apache Spark)
> Physical Plan Differences when Table Scan Having Duplicate Columns
> ------------------------------------------------------------------
>
> Key: SPARK-16594
> URL: https://issues.apache.org/jira/browse/SPARK-16594
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.0.0
> Reporter: Xiao Li
>
> Currently, we keep two implementations for planning scans over data sources. There is one difference between two implementation when deciding whether a `Project` is needed or not.
> - Data Source Table Scan: https://github.com/apache/spark/blob/b1e5281c5cb429e338c3719c13c0b93078d7312a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSourceStrategy.scala#L322-L395
> - `SELECT b, b FROM oneToTenPruned`: **_Add `ProjectExec`._**
> - Hive Table Scan and In-memory Table Scan:
> https://github.com/apache/spark/blob/865ec32dd997e63aea01a871d1c7b4947f43c111/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkPlanner.scala#L71-L99
> - `SELECT b, b FROM oneToTenPruned`: **_No `ProjectExec` is added._**
> **Note.** When alias is being used, we will always add `ProjectExec` in all the scan types.
> - `SELECT b as alias_b, b FROM oneToTenPruned`: **_Add `ProjectExec`._**
> Because selecting the same column twice without adding `alias` is very weird, no clue why the code needs to behave differently here.
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