[jira] [Assigned] (IMPALA-7967) Incorrect decimal size in V2 for a numeric const cast to BIGINT

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

     [ https://issues.apache.org/jira/browse/IMPALA-7967?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Paul Rogers reassigned IMPALA-7967:
-----------------------------------

    Assignee:     (was: Paul Rogers)

> Incorrect decimal size in V2 for a numeric const cast to BIGINT
> ---------------------------------------------------------------
>
>                 Key: IMPALA-7967
>                 URL: https://issues.apache.org/jira/browse/IMPALA-7967
>             Project: IMPALA
>          Issue Type: Bug
>          Components: Frontend
>    Affects Versions: Impala 3.1.0
>            Reporter: Paul Rogers
>            Priority: Major
>
> Decimal version 2 introduces revised rules for computing decimal width. For example:
> {noformat}
> CAST(1 AS DECIMAL(10, 0)) + CAST(2 AS DECIMAL(19,0)) --> DECIMAL(20,0)
> {noformat}
> The FE uses rules to convert from one type to another. The rule to convert from {{BIGINT}} to {{DECIMAL}} is:
> {noformat}
> BIGINT --> DECIMAL(19,0)
> {noformat}
> Put these two together:
> {noformat}
> CAST(1 AS DECIMAL(10, 0)) + CAST(2 AS BIGINT)
> {noformat}
> The result should be {{DECIMAL(20,0)}}. But, because of a bug in the way constant folding works, the result is actually {{DECIMAL(11,0)}} as seen in {{AnalyzeExprsTest.TestDecimalArithmetic()}}:
> {code:java}
>     testDecimalExpr(decimal_10_0 + " + cast(1 as bigint)",
>         ScalarType.createDecimalType(11, 0));
> {code}
> It seems one reason the bug was not caught is that the unit tests only check for constants, not for columns. Modify the tests to work against {{functional.alltypes}} (they currently work without a table), and substitute {{bigint_col}} for {{CAST(2 AS BIGINT)}}.
> Expected that the code should have followed the rules described above whether the values are a column, or a constant explicitly cast to the same type as the column. (Constants without out a cast should follow rules for their "natural type" which is what appears to be incorrectly happening in the test case above.)



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