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From "Bryan Pendleton (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3975) SELECT DISTINCT may return duplicates with territory-based collation
Date Tue, 09 Dec 2008 14:30:45 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3975?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12654807#action_12654807
] 

Bryan Pendleton commented on DERBY-3975:
----------------------------------------

What are the upgrade implications of changing the hash code implementations of a data type?


> SELECT DISTINCT may return duplicates with territory-based collation
> --------------------------------------------------------------------
>
>                 Key: DERBY-3975
>                 URL: https://issues.apache.org/jira/browse/DERBY-3975
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.4.2.0
>            Reporter: Knut Anders Hatlen
>            Assignee: Knut Anders Hatlen
>         Attachments: AisBCollatorProvider.java
>
>
> I defined my own locale (en_US_aisb) where the collation rules said that a=b. When I
tried queries with SELECT DISTINCT, they didn't always eliminate all duplicates. Here's an
example:
> ij> connect 'jdbc:derby:db;create=true;territory=en_US_aisb;collation=TERRITORY_BASED';
> ij> create table t (x varchar(10));
> 0 rows inserted/updated/deleted
> ij> insert into t values 'a','b','abba','baab','ABBA';
> 5 rows inserted/updated/deleted
> ij> select distinct * from t;
> X         
> ----------
> ABBA      
> b         
> a         
> abba      
> 4 rows selected
> ij> select distinct * from t order by x;
> X         
> ----------
> a         
> abba      
> ABBA      
> 3 rows selected
> The first query did eliminate the duplicate "abba"/"baab", but it did not eliminate the
duplicate "a"/"b". When an ORDER BY clause was added (the second query), all the duplicates
were eliminated.

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