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https://issues.apache.org/jira/browse/CALCITE-845?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14959620#comment-14959620
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James Taylor commented on CALCITE-845:
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[~maryannxue] - this is the JIRA that will help make our SUM aggregation to
work, since we coerce to a long any sum over integer numbers.
> Derive SUM’s return type by a customizable policy
> -------------------------------------------------
>
> Key: CALCITE-845
> URL: https://issues.apache.org/jira/browse/CALCITE-845
> Project: Calcite
> Issue Type: Bug
> Reporter: liyang
> Assignee: Julian Hyde
>
> The purpose is to return correct sum result when the number goes beyond its
> type limitation. Currently Calcite behaves "type sum( x ) = type x", so if
> the sum overflows, user get negative result.
> Traditional SQL engines all expand the sum return type though in different
> ways.
> From [~julianhyde], Aug 11:
> {quote}
> Postgres return type is "bigint for smallint or int arguments, numeric for
> bigint arguments, otherwise the same as the argument data type” [
> http://docs.oracle.com/database/121/SQLRF/functions196.htm#i89126 ]
> SQL Server return type is int for tinyint, smallint or int; bigint for bigint
> [
> http://public.dhe.ibm.com/ps/products/db2/info/vr101/pdf/en_US/DB2SQLRefVol1-db2s1e1011.pdf
> ].
> I can see your point that “User demands the correct sum result”. But I’d also
> be pissed with Postgres if it returned a numeric (arbitrary precision) result
> when I am summing a bigint value. So I don’t think we’re going to please
> everyone.
> I think the solution is to add the policy to derive SUM’s return type to as a
> new method to RelDataTypeSystem. Then Kylin can supply its own.
> {quote}
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