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https://issues.apache.org/jira/browse/DERBY-5959?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13481411#comment-13481411
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Knut Anders Hatlen commented on DERBY-5959:
-------------------------------------------
Example where this would lead to inconsistencies:
Create a database using Java 5:
connect
'jdbc:derby:tr-db;territory=tr_TR;collation=TERRITORY_BASED;create=true';
create table t(c char(2));
insert into t values 'ıa', 'Ia', 'ia', 'İa', 'ıb', 'Ib', 'ib', 'İb';
create unique index idx on t(c);
Then update the database using Java 6 or later:
connect 'jdbc:derby:tr-db';
insert into t values 'ıb';
select * from t;
The result of the SELECT statement is:
ij> select * from t;
C
----
ıa
Ia
ıb
ia
İa
ıb
Ib
ib
İb
9 rows selected
The value 'ıb' appears twice, even though there is a unique index on the column.
> Territory-based collation is not robust against changes in the collation rules
> ------------------------------------------------------------------------------
>
> Key: DERBY-5959
> URL: https://issues.apache.org/jira/browse/DERBY-5959
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.10.0.0
> Reporter: Knut Anders Hatlen
>
> When accessing a database with territory-based collation, Derby will use the
> collation rules of the collator returned by
> Collator.getInstance(databaseLocale). However, there is no guarantee that
> those rules are consistent across different JVM vendors and versions. This
> means that the ordering could vary, and inconsistencies could sneak into the
> indexes.
> One example is that Oracle's JDK changed the collation rules for Turkish
> between Java 5 and Java 6, so if you run the following script
> connect
> 'jdbc:derby:memory:db;territory=tr_TR;collation=TERRITORY_BASED;create=true';
> create table t(c char(2));
> insert into t values 'ıa', 'Ia', 'ia', 'İa', 'ıb', 'Ib', 'ib', 'İb';
> select * from t order by c;
> you'll get different results on Java 5 and on Java 6 and later.
> Java 5 will order the results like this:
> ij> select * from t order by c;
> C
> ----
> ıa
> Ia
> ia
> İa
> ıb
> Ib
> ib
> İb
> 8 rows selected
> Java 6 and later order them like this like this:
> ij> select * from t order by c;
> C
> ----
> ıa
> Ia
> ıb
> Ib
> ia
> İa
> ib
> İb
> 8 rows selected
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