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Posted to issues@spark.apache.org by "Cheng Lian (JIRA)" <ji...@apache.org> on 2016/04/08 18:03:25 UTC
[jira] [Updated] (SPARK-14488) "CREATE TEMPORARY TABLE ... USING
... AS SELECT ..." creates persisted table
[ https://issues.apache.org/jira/browse/SPARK-14488?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Cheng Lian updated SPARK-14488:
-------------------------------
Summary: "CREATE TEMPORARY TABLE ... USING ... AS SELECT ..." creates persisted table (was: Weird behavior of DDL "CREATE TEMPORARY TABLE ... USING ... AS SELECT ...")
> "CREATE TEMPORARY TABLE ... USING ... AS SELECT ..." creates persisted table
> ----------------------------------------------------------------------------
>
> Key: SPARK-14488
> URL: https://issues.apache.org/jira/browse/SPARK-14488
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.0.0
> Reporter: Cheng Lian
> Assignee: Cheng Lian
>
> Currently, Spark 2.0 master allows DDL statements like {{CREATE TEMPORARY TABLE ... USING ... AS SELECT ...}}, which imposes weird behavior and weird semantics.
> Let's try the following Spark shell snippet:
> {code}
> sqlContext range 10 registerTempTable "x"
> // The problematic DDL statement:
> sqlContext sql "CREATE TEMPORARY TABLE y USING PARQUET AS SELECT * FROM x"
> sqlContext.tables().show()
> {code}
> It shows the following result:
> {noformat}
> +---------+-----------+
> |tableName|isTemporary|
> +---------+-----------+
> | y| false|
> | x| true|
> +---------+-----------+
> {noformat}
> *Weird behavior*
> Note that {{y}} is NOT temporary although it's created using {{CREATE TEMPORARY TABLE ...}}, and the query result is written in Parquet format under default Hive warehouse location, which is {{/user/hive/warehouse/y}} on my local machine.
> *Weird semantics*
> Secondly, even if this DDL statement does create a temporary table, the semantics is still somewhat weird:
> # It has a {{AS SELECT ...}} clause, which is supposed to run a given query instead of loading data from existing files.
> # It has a {{USING <format>}} clause, which is supposed to, I guess, converting the result of the above query into the given format. And by "converting", we have to write out the data into file system.
> # It has a {{TEMPORARY}} keyword, which is supposed to, I guess, create an in-memory temporary table using the files written above?
> The main questions:
> # Is the above combination ({{TEMPORARY}} + {{USING}} + {{AS SELECT}}) a valid one?
> # If it's not, why do we have a [{{CreateTempTableUsingAsSelect}} command|https://github.com/apache/spark/blob/583b5e05309adb73cdffd974a810d6bfb5f2ff95/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/ddl.scala#L116], which exactly maps to this combination?
> # If it is, what is the expected semantics?
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