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https://issues.apache.org/jira/browse/HIVE-5356?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Xuefu Zhang updated HIVE-5356:
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Description:
Currently, all of the arithmetic operators, such as add/sub/mult/div, are
implemented as old-style UDFs and java reflection is used to determine the
return type TypeInfos/ObjectInspectors, based on the return type of the
evaluate() method chosen for the expression. This works fine for types that
don't have type params.
Hive decimal type participates in these operations just like int or double.
Different from double or int, however, decimal has precision and scale, which
cannot be determined by just looking at the return type (decimal) of the UDF
evaluate() method, even though the operands have certain precision/scale. With
the default of "decimal" without precision/scale, then (10, 0) will be the type
params. This is certainly not desirable.
To solve this problem, all of the arithmetic operators would need to be
implemented as GenericUDFs, which allow returning ObjectInspector during the
initialize() method. The object inspectors returned can carry type params, from
which the "exact" return type can be determined.
It's worth mentioning that, for user UDF implemented in non-generic way, if the
return type of the chosen evaluate() method is decimal, the return type
actually has (10,0) as precision/scale, which might not be desirable. This
needs to be documented.
This JIRA will cover minus, plus, divide, multiply, mod, and pmod, to limit the
scope of review. The remaining ones will be covered under HIVE-5706.
was:
Currently, all of the arithmetic operators, such as add/sub/mult/div, are
implemented as old-style UDFs and java reflection is used to determine the
return type TypeInfos/ObjectInspectors, based on the return type of the
evaluate() method chosen for the expression. This works fine for types that
don't have type params.
Hive decimal type participates in these operations just like int or double.
Different from double or int, however, decimal has precision and scale, which
cannot be determined by just looking at the return type (decimal) of the UDF
evaluate() method, even though the operands have certain precision/scale. With
the default of "decimal" without precision/scale, then (10, 0) will be the type
params. This is certainly not desirable.
To solve this problem, all of the arithmetic operators would need to be
implemented as GenericUDFs, which allow returning ObjectInspector during the
initialize() method. The object inspectors returned can carry type params, from
which the "exact" return type can be determined.
It's worth mentioning that, for user UDF implemented in non-generic way, if the
return type of the chosen evaluate() method is decimal, the return type
actually has (10,0) as precision/scale, which might not be desirable. This
needs to be documented.
> Move arithmatic UDFs to generic UDF implementations
> ---------------------------------------------------
>
> Key: HIVE-5356
> URL: https://issues.apache.org/jira/browse/HIVE-5356
> Project: Hive
> Issue Type: Task
> Components: UDF
> Affects Versions: 0.11.0
> Reporter: Xuefu Zhang
> Assignee: Xuefu Zhang
> Fix For: 0.13.0
>
>
> Currently, all of the arithmetic operators, such as add/sub/mult/div, are
> implemented as old-style UDFs and java reflection is used to determine the
> return type TypeInfos/ObjectInspectors, based on the return type of the
> evaluate() method chosen for the expression. This works fine for types that
> don't have type params.
> Hive decimal type participates in these operations just like int or double.
> Different from double or int, however, decimal has precision and scale, which
> cannot be determined by just looking at the return type (decimal) of the UDF
> evaluate() method, even though the operands have certain precision/scale.
> With the default of "decimal" without precision/scale, then (10, 0) will be
> the type params. This is certainly not desirable.
> To solve this problem, all of the arithmetic operators would need to be
> implemented as GenericUDFs, which allow returning ObjectInspector during the
> initialize() method. The object inspectors returned can carry type params,
> from which the "exact" return type can be determined.
> It's worth mentioning that, for user UDF implemented in non-generic way, if
> the return type of the chosen evaluate() method is decimal, the return type
> actually has (10,0) as precision/scale, which might not be desirable. This
> needs to be documented.
> This JIRA will cover minus, plus, divide, multiply, mod, and pmod, to limit
> the scope of review. The remaining ones will be covered under HIVE-5706.
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