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From "Daniel John Debrunner (JIRA)" <derby-...@db.apache.org>
Subject [jira] Commented: (DERBY-533) Re-enable national character datatypes
Date Wed, 24 Aug 2005 18:43:14 GMT
    [ http://issues.apache.org/jira/browse/DERBY-533?page=comments#action_12319893 ] 

Daniel John Debrunner commented on DERBY-533:
---------------------------------------------

I can think of two issues.

1) JDBC constants (java.sql.Types) do not exist for these types until JDBC 4.0.

2) In the existing code, conversions of national character types to and from datetime and
number types applied localization.
I don't know if this approach is correct with respect to the SQL standard, or in-line with
other databases. Ensuring conversions
are correct before allow applications to use them  was the reason for disabling them. Didn't
want to get into some backwards
compatibility issues by changing the behaviour to match the standard. I don't think anyone
had time to resolve this.
An example would be converting a DECIMAL of 1.2, to VARCHAR the conversion is 1.2, but in
a French database the conversion
to NATIONAL VARCHAR would be 1,2. Is this correct? Similar for conversions from character
types, should 1,2 be converted
to 1.2 in French from a NATIONAL VARCHAR? This is from memory, I know this is true for the
datetime types, but  maybe isn't
true for the numeric types (but they are easier to explain and come up with simple examples
:-).
          

> 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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