5.2. Multibyte Support

5.2.1. Enabling MB

Run configure with the multibyte option:

% ./configure --enable-multibyte[=encoding_system]
     

Here is an example of configuring Postgres to use a Japanese encoding by default:

% ./configure --enable-multibyte=EUC_JP
     

If the encoding system is omitted (./configure --enable-multibyte), SQL_ASCII is assumed.

5.2.2. Setting the Encoding

initdb defines the default encoding for a Postgres installation. For example:

% initdb -E EUC_JP
     

You can create a database with a different encoding:

% createdb -E EUC_KR korean
     

CREATE DATABASE korean WITH ENCODING = 'EUC_KR';
     

$ psql -l
            List of databases
   Database    |  Owner  |   Encoding    
---------------+---------+---------------
 euc_cn        | t-ishii | EUC_CN
 euc_jp        | t-ishii | EUC_JP
 euc_kr        | t-ishii | EUC_KR
 euc_tw        | t-ishii | EUC_TW
 mule_internal | t-ishii | MULE_INTERNAL
 regression    | t-ishii | SQL_ASCII
 template1     | t-ishii | EUC_JP
 test          | t-ishii | EUC_JP
 unicode       | t-ishii | UNICODE
(9 rows)
     

5.2.3. Automatic encoding translation between backend and frontend

Postgres supports an automatic encoding translation between backend and frontend for some encodings.

To enable the automatic encoding translation, you have to tell Postgres the encoding you would like to use in frontend. There are several ways to accomplish this.

• Using the \encoding command in psql. \encoding allows you to change frontend encoding on the fly. For example, to change the encoding to SJIS, type:

  \encoding SJIS
          
  

• Using libpq functions. \encoding actually calls PQsetClientEncoding() for its purpose.

  int PQsetClientEncoding(PGconn *conn, const char *encoding)
          
  

  where conn is a connection to the backend, and encoding is an encoding you want to use. If it successfully sets the encoding, it returns 0, otherwise -1. The current encoding for this connection can be shown by using:

  int PQclientEncoding(const PGconn *conn)
          
  

  Note that it returns the "encoding id," not the encoding symbol string such as "EUC_JP." To convert an encoding id to an encoding symbol, you can use:

  char *pg_encoding_to_char(int encoding_id)
          
  

• Using SET CLIENT_ENCODING TO. Setting the frontend side encoding can be done by this SQL command:

  SET CLIENT_ENCODING TO 'encoding';
          
  

  Also you can use SQL92 syntax "SET NAMES" for this purpose:

  SET NAMES 'encoding';
          
  

  To query the current frontend encoding:

  SHOW CLIENT_ENCODING;
          
  

  To return to the default encoding:

  RESET CLIENT_ENCODING;
          
  

• Using PGCLIENTENCODING. If environment variable PGCLIENTENCODING is defined in the client's environment, that client encoding is automatically selected when a backend connection is made. (This can subsequently be overridden using any of the other methods mentioned above.)

5.2.4. About Unicode

An automatic encoding translation between Unicode and other encodings has been supported since PostgreSQL 7.1. Because this requires huge conversion tables, it's not enabled by default. To enable this feature, run configure with the --enable-unicode-conversion option. Note that this requires the --enable-multibyte option also.

5.2.5. What happens if the translation is not possible?

Suppose you choose EUC_JP for the backend, LATIN1 for the frontend, then some Japanese characters could not be translated into LATIN1. In this case, a letter that cannot be represented in the LATIN1 character set would be transformed as:

(HEXA DECIMAL)
     

5.2.6. References

These are good sources to start learning about various kinds of encoding systems.

• ftp://ftp.ora.com/pub/examples/nutshell/ujip/doc/cjk.inf Detailed explanations of EUC_JP, EUC_CN, EUC_KR, EUC_TW appear in section 3.2.

• Unicode: http://www.unicode.org/ The homepage of UNICODE.

• RFC 2044 UTF-8 is defined here.

5.2.7. History

Dec 7, 2000
        * An automatic encoding translation between Unicode and other
          encodings are implemented
        * Changes above will appear in 7.1

May 20, 2000
        * SJIS UDC (NEC selection IBM kanji) support contributed
          by Eiji Tokuya
        * Changes above will appear in 7.0.1

Mar 22, 2000
        * Add new libpq functions PQsetClientEncoding, PQclientEncoding
        * ./configure --with-mb=EUC_JP
          now deprecated. use 
          ./configure --enable-multibyte=EUC_JP
          instead
        * Add SQL_ASCII regression test case
        * Add SJIS User Defined Character (UDC) support
        * All of above will appear in 7.0

July 11, 1999
        * Add support for WIN1250 (Windows Czech) as a client encoding
          (contributed by Pavel Behal)
        * fix some compiler warnings (contributed by Tomoaki Nishiyama)

Mar 23, 1999
        * Add support for KOI8(KOI8-R), WIN(CP1251), ALT(CP866)
          (thanks Oleg Broytmann for testing)
        * Fix problem with MB and locale

Jan 26, 1999
        * Add support for Big5 for fronend encoding
          (you need to create a database with EUC_TW to use Big5)
        * Add regression test case for EUC_TW
          (contributed by Jonah Kuo <[email protected]>)

Dec 15, 1998
        * Bugs related to SQL_ASCII support fixed

Nov 5, 1998
        * 6.4 release. In this version, pg_database has "encoding"
          column that represents the database encoding

Jul 22, 1998
        * determine encoding at initdb/createdb rather than compile time
        * support for PGCLIENTENCODING when issuing COPY command
        * support for SQL92 syntax "SET NAMES"
        * support for LATIN2-5
        * add UNICODE regression test case
        * new test suite for MB
        * clean up source files

Jun 5, 1998
        * add support for the encoding translation between the backend
          and the frontend
        * new command SET CLIENT_ENCODING etc. added
        * add support for LATIN1 character set
        * enhance 8 bit cleaness

April 21, 1998 some enhancements/fixes
        * character_length(), position(), substring() are now aware of 
          multi-byte characters
        * add octet_length()
        * add --with-mb option to configure
        * new regression tests for EUC_KR
          (contributed by Soonmyung Hong <[email protected]>)
        * add some test cases to the EUC_JP regression test
        * fix problem in regress/regress.sh in case of System V
        * fix toupper(), tolower() to handle 8bit chars

Mar 25, 1998 MB PL2 is incorporated into PostgreSQL 6.3.1

Mar 10, 1998 PL2 released
        * add regression test for EUC_JP, EUC_CN and MULE_INTERNAL
        * add an English document (this file)
        * fix problems concerning 8-bit single byte characters

Mar 1, 1998 PL1 released
     

5.2.8. WIN1250 on Windows/ODBC

The WIN1250 character set on Windows client platforms can be used with Postgres with locale support enabled.

The following should be kept in mind:

• Success depends on proper system locales. This has been tested with RH6.0 and Slackware 3.6, with cs_CZ.iso8859-2 locale.

• Never try to set the server multibyte database encoding to WIN1250. Always use LATIN2 instead since there is not a WIN1250 locale in Unix.

• WIN1250 encoding is useable only for M$W ODBC clients. The characters are recoded on the fly, to be displayed and stored back properly.

When running, it is important to remember the following:

• This configuration reorders your sort order depending on your LC_x settings. Don't be confused with the regression test results since they don't use locale.

• A locale such as "ch" is correctly sorted only if your system supports that locale; older systems may not do so but new ones (e.g. RH6.0) do.

• You have to insert money as '162,50' (note comma within the single-quotes).

• At the time of writing (early 1999), this configuration has not received extensive testing. Please let us know of any changes you had to make!