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From: "MauMau" <maumau307@gmail.com>
To: "Greg Stark" <stark@mit.edu>
Cc: "Peter Eisentraut" <peter_e@gmx.net>,
 "Robert Haas" <robertmhaas@gmail.com>,
 "Tatsuo Ishii" <ishii@postgresql.org>, "Tom Lane" <tgl@sss.pgh.pa.us>,
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Subject: Re: UTF8 national character data type support WIP patch and list of
 open issues.
Date: Thu, 26 Sep 2013 06:18:10 +0900
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From: "Greg Stark" <stark@mit.edu>
> If it's not lossy then what's the point? From the client's point of view
> it'll be functionally equivalent to text then.

Sorry, what Tatsuo san suggested meant was "same or compatible", not lossy. 
I quote the relevant part below.  This is enough for the use case I 
mentioned in my previous mail several hours ago (actually, that is what 
Oracle manual describes...).

http://www.postgresql.org/message-id/20130920.085853.1628917054830864151.t-ishii@sraoss.co.jp

[Excerpt]
----------------------------------------
What about limiting to use NCHAR with a database which has same
encoding or "compatible" encoding (on which the encoding conversion is
defined)? This way, NCHAR text can be automatically converted from
NCHAR to the database encoding in the server side thus we can treat
NCHAR exactly same as CHAR afterward.  I suppose what encoding is used
for NCHAR should be defined in initdb time or creation of the database
(if we allow this, we need to add a new column to know what encoding
is used for NCHAR).

For example, "CREATE TABLE t1(t NCHAR(10))" will succeed if NCHAR is
UTF-8 and database encoding is UTF-8. Even succeed if NCHAR is
SHIFT-JIS and database encoding is UTF-8 because there is a conversion
between UTF-8 and SHIFT-JIS. However will not succeed if NCHAR is
SHIFT-JIS and database encoding is ISO-8859-1 because there's no
conversion between them.
----------------------------------------


Regards
MauMau



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