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From "HBase Review Board (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-537) Hive TypeInfo/ObjectInspector to support union (besides struct, array, and map)
Date Mon, 20 Sep 2010 09:57:33 GMT

    [ https://issues.apache.org/jira/browse/HIVE-537?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12912420#action_12912420
] 

HBase Review Board commented on HIVE-537:
-----------------------------------------

Message from: "Amareshwari Sriramadasu" <amarsri@yahoo-inc.com>


bq.  On 2010-09-15 15:15:08, Zheng Shao wrote:
bq.  > Overall looks like a good first step.  We need to change Hive.g, add UDF etc to
allow users to use it in the Hive language.

Zheng, there is already keyword (KW_UNION: 'UNION') used for doing union/union all operations.
Do you think we should use a different keyword for specifying Union type?


- Amareshwari


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> Hive TypeInfo/ObjectInspector to support union (besides struct, array, and map)
> -------------------------------------------------------------------------------
>
>                 Key: HIVE-537
>                 URL: https://issues.apache.org/jira/browse/HIVE-537
>             Project: Hadoop Hive
>          Issue Type: New Feature
>            Reporter: Zheng Shao
>            Assignee: Amareshwari Sriramadasu
>         Attachments: HIVE-537.1.patch, patch-537-1.txt, patch-537.txt
>
>
> There are already some cases inside the code that we use heterogeneous data: JoinOperator,
and UnionOperator (in the sense that different parents can pass in records with different
ObjectInspectors).
> We currently use Operator's parentID to distinguish that. However that approach does
not extend to more complex plans that might be needed in the future.
> We will support the union type like this:
> {code}
> TypeDefinition:
>   type: primitivetype | structtype | arraytype | maptype | uniontype
>   uniontype: "union" "<" tag ":" type ("," tag ":" type)* ">"
> Example:
>   union<0:int,1:double,2:array<string>,3:struct<a:int,b:string>>
> Example of serialized data format:
>   We will first store the tag byte before we serialize the object. On deserialization,
we will first read out the tag byte, then we know what is the current type of the following
object, so we can deserialize it successfully.
> Interface for ObjectInspector:
> interface UnionObjectInspector {
>   /** Returns the array of OIs that are for each of the tags
>    */
>   ObjectInspector[] getObjectInspectors();
>   /** Return the tag of the object.
>    */
>   byte getTag(Object o);
>   /** Return the field based on the tag value associated with the Object.
>    */
>   Object getField(Object o);
> };
> An example serialization format (Using deliminated format, with ' ' as first-level delimitor
and '=' as second-level delimitor)
> userid:int,log:union<0:struct<touserid:int,message:string>>,1:string>
> 123 1=login
> 123 0=243=helloworld
> 123 1=logout
> {code}

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