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https://issues.apache.org/jira/browse/HIVE-15434?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Lefty Leverenz updated HIVE-15434:
----------------------------------
Labels: TODOC2.3 (was: )
> Add UDF to allow interrogation of uniontype values
> --------------------------------------------------
>
> Key: HIVE-15434
> URL: https://issues.apache.org/jira/browse/HIVE-15434
> Project: Hive
> Issue Type: New Feature
> Components: UDF
> Affects Versions: 2.1.1
> Reporter: David Maughan
> Assignee: David Maughan
> Labels: TODOC2.3
> Fix For: 2.3.0, 3.0.0
>
> Attachments: HIVE-15434.01.patch, HIVE-15434.02.patch
>
>
> h2. Overview
> As stated in the documention:
> {quote}
> UNIONTYPE support is incomplete The UNIONTYPE datatype was introduced in Hive
> 0.7.0 (HIVE-537), but full support for this type in Hive remains incomplete.
> Queries that reference UNIONTYPE fields in JOIN (HIVE-2508), WHERE, and GROUP
> BY clauses will fail, and Hive does not define syntax to extract the tag or
> value fields of a UNIONTYPE. This means that UNIONTYPEs are effectively
> look-at-only.
> {quote}
> It is essential to have a usable uniontype. Until full support is added to
> Hive users should at least have the ability to inspect and extract values for
> further comparison or transformation.
> h2. Proposal
> I propose to add a GenericUDF that has 2 modes of operation. Consider the
> following schema and data that contains a union:
> Schema:
> {code}
> struct<field1:uniontype<int,string>>
> {code}
> Query:
> {code}
> hive> select field1 from thing;
> {0:0}
> {1:"one"}
> {code}
> h4. Explode to Struct
> This method will recursively convert all unions within the type to structs
> with fields named {{tag_n}}, {{n}} being the tag number. Only the {{tag_*}}
> field that matches the tag of the union will be populated with the value. In
> the case above the schema of field1 will be converted to:
> {code}
> struct<tag_0:int,tag_1:string>
> {code}
> {code}
> hive> select extract_union(field1) from thing;
> {"tag_0":0,"tag_1":null}
> {"tag_0":null,"tag_1":one}
> {code}
> {code}
> hive> select extract_union(field1).tag_0 from thing;
> 0
> null
> {code}
> h4. Extract the specified tag
> This method will simply extract the value of the specified tag. If the tag
> number matches then the value is returned, if it does not, then null is
> returned.
> {code}
> hive> select extract_union(field1, 0) from thing;
> 0
> null
> {code}
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