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 <[email protected]> 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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