[jira] [Created] (HIVE-22513) Constant propagation of casted column in filter ops can cause incorrect results

["Ádám Szita (Jira)" <ji...@apache.org>]

Ádám Szita created HIVE-22513:
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             Summary: Constant propagation of casted column in filter ops can cause incorrect results
                 Key: HIVE-22513
                 URL: https://issues.apache.org/jira/browse/HIVE-22513
             Project: Hive
          Issue Type: Bug
            Reporter: Ádám Szita
            Assignee: Ádám Szita


This issue happens if CBO is disabled.

We should not be propagating constants if the corresponding ExprNodeColumnDesc instance is wrapped inside a CAST operator as casting might truncate information from the original column.

This can happen if we're using CAST in a WHERE clause, which will cause the projected columns to be replaced in a SELECT operator. Their new value will be the result of casting which could be a different value compared to that in the original column:
{code:java}
set hive.cbo.enable=false;
set hive.fetch.task.conversion=more; --just for testing convenience
create table testtb (id string);
insert into testtb values('2019-11-05 01:01:11');
select id, CAST(id AS VARCHAR(10)) from testtb where CAST(id AS VARCHAR(9)) = '2019-11-0';

+------------+------------+
|     id     |    _c1     |
+------------+------------+
| 2019-11-0  | 2019-11-0  |
+------------+------------+
1 row selected (0.168 seconds)

-- VS expected: 2019-11-05 01:01:11 | 2019-11-05 {code}
As to what types of casting (from and where types) cause information loss it's hard to properly keep track of, and I don't think it should be taken into consideration when deciding whether or not to propagate a constant. Rather than adding a big and potentially convoluted and fragile check for this, I propose to prevent constant mappings to be spawned out of CASTed columns.



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