David Maughan created HIVE-15434:
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Summary: Hive GenericUDF to make uniontype more usable
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
Priority: Minor
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 would be useful to have a UDF that allows extraction of 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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