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Jason Dere commented on HIVE5356:

Nice. I was playing with the patch and had some questions about the return typeInfo when
using decimal with nondecimals:
{noformat}
hive> explain select cast(1 as decimal(10,2)) / cast(1 as decimal(10,2)) from src;
...
expressions:
expr: (CAST( 1 AS decimal(10,2)) / CAST( 1 AS decimal(10,2)))
type: decimal(23,13)
{noformat}
Ok so far.
{noformat}
hive> explain select cast(1 as decimal(10,2)) / cast(1 as decimal(10,2)) /2 from src;
...
expressions:
expr: ((CAST( 1 AS decimal(10,2)) / CAST( 1 AS decimal(10,2))) / 2)
type: double
{noformat}
Maybe we can keep the result type as decimal when possible? At least when the other argument
is also exact numeric (int, short, etc).
> 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
>
> Attachments: HIVE5356.patch
>
>
> 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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