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https://issues.apache.org/jira/browse/DERBY-2967?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12518262
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Daniel John Debrunner commented on DERBY-2967:
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I would say neither (existing or proposed)  is correct, though only after 
looking at your example.

The existing code is wrong because it is converting the '_' to a collation 
element then skipping that number of collation elements?

The proposed results are wrong because in the French locale agraveCombined 
="A\u0300" is a single character.
I assume the \u0300 is a 'Combining character'.

http://www.unicode.org/versions/Unicode5.0.0/ch03.pdf#G30602

Thus I think the results should be:

0 rows matching SELECT COUNT(*) FROM T WHERE VC LIKE A_
2 rows matching SELECT COUNT(*) FROM T WHERE VC LIKE _ (agrave,agraveCombined)
0 rows matching SELECT COUNT(*) FROM T WHERE VC LIKE __

As for implementing it, I think one has to use the getOffset/setOffset method 
on CollationElementIterator.

E.g. along the lines of this to skip a character. The real solution would be 
more than this but you get the idea.

   if (patternChar == '_')
       iterator.setOffset(iterator.getOffset() + 1);








> Single character does not match high value unicode character with collation 
> TERRITORY_BASED
> -------------------------------------------------------------------------------------------
>
>                 Key: DERBY-2967
>                 URL: https://issues.apache.org/jira/browse/DERBY-2967
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.4.0.0
>            Reporter: Kathey Marsden
>            Assignee: Kathey Marsden
>         Attachments: TestFrench.java
>
>
> With TERRITORY_BASED collation '_' does not match  the character \uFA2D.  It 
> is the same for english or norwegian. FOR collation UCS_BASIC it matches 
> fine.  Could you tell me if this is a bug?
> Here is a program to reproduce.
> import java.sql.*;
> public class HighCharacter {
>    public static void main(String args[]) throws Exception
>    {
>    System.out.println("\n Territory no_NO");
>    Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
>    Connection conn = 
> DriverManager.getConnection("jdbc:derby:nordb;create=true;territory=no_NO;collation=TERRITORY_BASED");
>    testLikeWithHighestValidCharacter(conn);
>    conn.close();
>    System.out.println("\n Territory en_US");
>    conn = 
> DriverManager.getConnection("jdbc:derby:endb;create=true;territory=en_US;collation=TERRITORY_BASED");
>    testLikeWithHighestValidCharacter(conn);
>    conn.close();
>    System.out.println("\n Collation USC_BASIC");
>    conn = DriverManager.getConnection("jdbc:derby:basicdb;create=true");
>    testLikeWithHighestValidCharacter(conn);
>    }
> public static  void testLikeWithHighestValidCharacter(Connection conn) throws 
> SQLException {
>    Statement stmt = conn.createStatement();
>    try {
>    stmt.executeUpdate("drop table t1");
>    }catch (SQLException se)
>    {// drop failure ok.
>    }
>    stmt.executeUpdate("create table t1(c11 int)");
>    stmt.executeUpdate("insert into t1 values 1");
>  
>    // \uFA2D - the highest valid character according to
>    // Character.isDefined() of JDK 1.4;
>    PreparedStatement ps =
>    conn.prepareStatement("select 1 from t1 where '\uFA2D' like ?");
>      String[] match = { "%", "_", "\uFA2D" };
>    for (int i = 0; i < match.length; i++) {
>    System.out.println("select 1 from t1 where '\\uFA2D' like " + match[i]);
>    ps.setString(1, match[i]);
>    ResultSet rs = ps.executeQuery();
>    if( rs.next() && rs.getString(1).equals("1"))
>        System.out.println("PASS");
>    else          System.out.println("FAIL: no match");
>    rs.close();
>    }
>   }
> }
> Mamta made some comments on this issue in the following thread:
> http://www.nabble.com/Single-character-does-not-match-high-value-unicode-character-with-collation-TERRITORY_BASED.-Is-this-a-bug-tf4118767.html

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