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From "Rick Hillegas (JIRA)" <derby-...@db.apache.org>
Subject [jira] Created: (DERBY-533) Re-enable national character datatypes
Date Tue, 23 Aug 2005 23:13:08 GMT
Re-enable national character datatypes
--------------------------------------

         Key: DERBY-533
         URL: http://issues.apache.org/jira/browse/DERBY-533
     Project: Derby
        Type: New Feature
  Components: SQL  
    Versions: 10.1.1.0    
    Reporter: Rick Hillegas


SQL 2003 coyly defines national character types as "implementation defined". Accordingly,
there is considerable variability in how these datatypes behave. Oracle and MySQL use these
datatypes to store unicode strings. This would not distinguish national from non-national
character types in Derby since Derby stores all strings as unicode sequences.

The national character datatypes (NCHAR, NVARCHAR, NCLOB and their synonymns) used to exist
in Cloudscape but were disabled in Derby. The disabling comment in the grammar says "need
to re-enable according to SQL standard". Does this mean that the types were removed because
they chafed against SQL 2003? If so, what are their defects?

------------------------------------------------------------------

Cloudscape 3.5 provided the following support for national character types:

- NCHAR and NVARCHAR were legal datatypes.
- Ordering operations on these datatypes was determined by the collating sequence associated
with the locale of the database.
- The locale was a DATABASE-wide property which could not be altered.
- Ordering on non-national character datatypes was lexicographic, that is, character by character.

------------------------------------------------------------------

Oracle 9i provides the following support for national character types:

- NCHAR, NVARCHAR2, and NCLOB datatypes are used to store unicode strings.
- Sort order can be overridden per SESSION or even per QUERY, which means that these overridden
sort orders are not supported by indexes.

------------------------------------------------------------------

DB2 does not appear to support national character types. Nor does its DRDA data interchange
protocol.

------------------------------------------------------------------

MySQL provides the following support for national character types:

- National Char and National Varchar datatypes are used to hold unicode strings. I cannot
find a national CLOB type.
- The character set and sort order can be changed at SERVER-wide, TABLE-wide, or COLUMN-specific
levels.

------------------------------------------------------------------

If we removed the disabling logic in Derby, I believe that the following would happen:

- We would get NCHAR, NVARCHAR, and NCLOB datatypes.
- These would sort according to the locale that was bound to the database when it was created.
- We would have to build DRDA transport support for these types.

The difference between national and non-national datatypes would be their sort order.

I am keenly interested in understanding what defects (other than DRDA support) should be addressed
in the disabled implementation.


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