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https://issues.apache.org/jira/browse/HIVE-3976?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13754523#comment-13754523
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Jason Dere commented on HIVE-3976:
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One note about propagating precision/scale throughout the expressions,
especially if we want to have them available through jdbc/odbc. All of the
add/sub/mult/div operations are implemented as old-style UDFs, which is a bit
problematic. The old-style UDFs use reflection to determine the return type
TypeInfos/ObjectInspectors, based on the return type of the evaluate() method
chosen for the expression. The way this is being done, we cannot customize the
precision/scale of the TypeInfo representing the result - the resulting
TypeInfo would just be the default decimal type with no parameters, and
whatever default precision/scale information that comes with that type. So if
you want the type metadata to have the correctly set precision/scale, all of
the arithmetic operators would need to be redone as GenericUDFs, which allow
you to customize the return type ObjectInspector during the initialize()
method. I had to do the same thing with a few string UDFs to get the varchar
length reported back correctly in the TypeInfos.
> Support specifying scale and precision with Hive decimal type
> -------------------------------------------------------------
>
> Key: HIVE-3976
> URL: https://issues.apache.org/jira/browse/HIVE-3976
> Project: Hive
> Issue Type: Improvement
> Components: Query Processor, Types
> Reporter: Mark Grover
> Assignee: Xuefu Zhang
> Attachments: remove_prec_scale.diff
>
>
> HIVE-2693 introduced support for Decimal datatype in Hive. However, the
> current implementation has unlimited precision and provides no way to specify
> precision and scale when creating the table.
> For example, MySQL allows users to specify scale and precision of the decimal
> datatype when creating the table:
> {code}
> CREATE TABLE numbers (a DECIMAL(20,2));
> {code}
> Hive should support something similar too.
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