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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3975) SELECT DISTINCT may return duplicates with territory-based collation
Date Tue, 09 Dec 2008 14:38:44 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3975?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12654810#action_12654810

Knut Anders Hatlen commented on DERBY-3975:

I don't think we store the hash values anywhere, so to my knowledge they just have to be consistent
within the lifetime of the JVM. The only place I know that the hash values will go to disk,
is when a BackingStoreHashtable spills to disk, but that's just in a temporary file that will
be deleted on the next boot, as far as I know.

> 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:
>            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
> 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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