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https://issues.apache.org/jira/browse/HIVE-5356?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13813398#comment-13813398
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Jason Dere commented on HIVE-5356:
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Just want to point out to folks that this does result in some changes in return
type behavior for arithmetic operators, some of which were a bit of a surprise:
int / int => decimal
float / float => double
float * float => double
float + float => double
That said, this is still in line with what the SQL standard says about the
resulting type of these arithmetic operators (shown below), so I think this is
ok:
1) If the declared type of both operands of a dyadic arithmetic operator is
exact numeric, then the declared type of the result is an
implementation-defined exact numeric type, with precision and scale determined
as follows:
a) Let S1 and S2 be the scale of the first and second operands respectively.
b) The precision of the result of addition and subtraction is
implementation-defined, and the scale is the
maximum of S1 and S2.
c) The precision of the result of multiplication is implementation-defined, and
the scale is S1 + S2.
d) The precision and scale of the result of division are implementation-defined.
2) If the declared type of either operand of a dyadic arithmetic operator is
approximate numeric, then the declared type of the result is an
implementation-defined approximate numeric type.
> 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
>
> Attachments: HIVE-5356.1.patch, HIVE-5356.2.patch, HIVE-5356.patch
>
>
> 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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