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https://issues.apache.org/jira/browse/HIVE-24528?focusedWorklogId=523756&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-523756
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ASF GitHub Bot logged work on HIVE-24528:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 14/Dec/20 08:56
Start Date: 14/Dec/20 08:56
Worklog Time Spent: 10m
Work Description: zabetak opened a new pull request #1771:
URL: https://github.com/apache/hive/pull/1771
### What changes were proposed in this pull request?
Convert to decimal (instead of double) when comparing decimals and strings.
### Why are the changes needed?
Fix unexpected (by some considered wrong) query results and handle better
precision loss (examples in HIVE-24528)
### Does this PR introduce _any_ user-facing change?
Yes, this is a breaking change and query results when comparing decimals and
strings may change.
### How was this patch tested?
`mvn test -Dtest=TestMiniLlapLocalCliDriver -Dqfile="dec_str.q"`
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Issue Time Tracking
-------------------
Worklog Id: (was: 523756)
Remaining Estimate: 0h
Time Spent: 10m
> Wrong implicit type conversion when comparing decimals and strings
> ------------------------------------------------------------------
>
> Key: HIVE-24528
> URL: https://issues.apache.org/jira/browse/HIVE-24528
> Project: Hive
> Issue Type: Bug
> Components: HiveServer2
> Affects Versions: 2.3.0
> Reporter: Stamatis Zampetakis
> Assignee: Stamatis Zampetakis
> Priority: Major
> Time Spent: 10m
> Remaining Estimate: 0h
>
> In many cases when comparing decimals and strings (literals/columns) the
> comparison is done using doubles which can create some quite unexpected
> results in the answers of queries.
> {code:sql}
> create table t_str (str_col string);
> insert into t_str values ('1208925742523269458163819');
> select * from t_str where str_col=1208925742523269479013976;
> {code}
> The SELECT query brings up one row while the filtering value is not the same
> with the one present in the string column of the table. The problem is that
> both types are converted to doubles and due to loss of precision the values
> are deemed equal.
> The same happens during the join of a decimal with a string type.
> {code:sql}
> create table t_dec (dec_col decimal(25,0));
> insert into t_dec values (1208925742523269479013976);
> select * from t_dec inner join t_str on dec_col=str_col;
> {code}
> The join result contains one row although the values are not equal.
> Implicit type conversions are working differently in every DBMS and for some
> of them (e.g., mysql) the above behavior is normal or not allowed at all
> (e.g. Postgres).
> In the past, Hive used to compare decimal with string columns by converting
> to decimals but this behavior changed in 2.3.0 (with HIVE-13380). It seems
> that this behavior change was not intentional since following jiras (e.g.,
> HIVE-18434) imply that comparison of decimals with strings should be done
> using decimals. Since decimal is an exact numeric it appears a more
> appropriate type for comparing decimals and strings.
> The goal of this issue is to change the implicit conversion of decimals with
> strings to doubles and use decimals instead.
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