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https://issues.apache.org/jira/browse/HIVE-2390?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13086714#comment-13086714
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Jakob Homan commented on HIVE-2390:
-----------------------------------
Part of the problem is that the term union has been overloaded. In SQL it
means the actual set union of two compatible data types, whereas in Avro and
programming languages it means one value that can be at any one time an
instance of two or different types. Union was added as a full-on, first-class
type by its inclusion in ObjectInspector's Category enum. Is there any reason
not to expand this use to be more along the line of programming language's take
on unions? If so, it should be marked as not really being a first-class type.
If not, support for unions in all the serdes, in the grammar and in the
documentation should be provided.
I would lobby for expanding its support as it's an important type in Avro and
we're quite hobbled by the inability to manipulate unioned values. (Avro
handles nullable values by unioning them with their type T and null, but
Haivvreo transparently converts these just to the type and returns null where
appropriate. The problem lies in actual unions of non-null types, which are
less frequent but still valid.)
> LazyBinarySerde (and others) don't support unions
> -------------------------------------------------
>
> Key: HIVE-2390
> URL: https://issues.apache.org/jira/browse/HIVE-2390
> Project: Hive
> Issue Type: Bug
> Reporter: Jakob Homan
>
> When the union type was introduced, full support for it wasn't provided. For
> instance, when working with a union that gets passed to LazyBinarySerde:
> {noformat}Caused by: java.lang.RuntimeException: Unrecognized type: UNION
> at
> org.apache.hadoop.hive.serde2.lazybinary.LazyBinarySerDe.serialize(LazyBinarySerDe.java:468)
> at
> org.apache.hadoop.hive.serde2.lazybinary.LazyBinarySerDe.serializeStruct(LazyBinarySerDe.java:230)
> at
> org.apache.hadoop.hive.serde2.lazybinary.LazyBinarySerDe.serialize(LazyBinarySerDe.java:184)
> {noformat}
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