[ https://issues.apache.org/jira/browse/HIVE5356?page=com.atlassian.jira.plugin.system.issuetabpanels:alltabpanel
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Xuefu Zhang updated HIVE5356:

Description:
Currently, all of the arithmetic operators, such as add/sub/mult/div, are implemented as oldstyle
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 nongeneric 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 HIVE5706.
was:
Currently, all of the arithmetic operators, such as add/sub/mult/div, are implemented as oldstyle
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 nongeneric 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: HIVE5356
> URL: https://issues.apache.org/jira/browse/HIVE5356
> 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 oldstyle 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 nongeneric 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 HIVE5706.

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