[jira] [Created] (CALCITE-845) Derive SUM’s return type by a customizable policy

["liyang (JIRA)" <ji...@apache.org>]

liyang created CALCITE-845:
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             Summary: 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 Julian Hyde <jh...@apache.org> Aug 11
"""
Postgres return type is "bigint for smallint or int arguments, numeric for bigint arguments, otherwise the same as the argument data type”[1]

SQL Server return type is int for tinyint, smallint or int; bigint for bigint[2].

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.
"""



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