22.3.1. Supported Character Sets

Table 22-1 shows the character sets available for use inPostgreSQL.

Not all clientAPIs support all the listed character sets. For example, thePostgreSQL JDBC driver does not supportMULE_INTERNAL,LATIN6,LATIN8, andLATIN10.

TheSQL_ASCII setting behaves considerably differently from the other settings. When the server character set isSQL_ASCII, the server interprets byte values 0-127 according to the ASCII standard, while byte values 128-255 are taken as uninterpreted characters. No encoding conversion will be done when the setting isSQL_ASCII. Thus, this setting is not so much a declaration that a specific encoding is in use, as a declaration of ignorance about the encoding. In most cases, if you are working with any non-ASCII data, it is unwise to use theSQL_ASCII setting becausePostgreSQL will be unable to help you by converting or validating non-ASCII characters.

22.3.2. Setting the Character Set

initdb defines the default character set (encoding) for aPostgreSQL cluster. For example,

initdb -E EUC_JP

sets the default character set toEUC_JP (Extended Unix Code for Japanese). You can use--encoding instead of-E if you prefer longer option strings. If no-E or--encoding option is given,initdb attempts to determine the appropriate encoding to use based on the specified or default locale.

You can specify a non-default encoding at database creation time, provided that the encoding is compatible with the selected locale:

createdb -E EUC_KR -T template0 --lc-collate=ko_KR.euckr --lc-ctype=ko_KR.euckr korean

This will create a database namedkorean that uses the character setEUC_KR, and localeko_KR. Another way to accomplish this is to use this SQL command:

CREATE DATABASE korean WITH ENCODING 'EUC_KR' LC_COLLATE='ko_KR.euckr' LC_CTYPE='ko_KR.euckr' TEMPLATE=template0;

Notice that the above commands specify copying thetemplate0 database. When copying any other database, the encoding and locale settings cannot be changed from those of the source database, because that might result in corrupt data. For more information seeSection 21.3.

The encoding for a database is stored in the system catalogpg_database. You can see it by using thepsql-l option or the\l command.

$psql -l                                         List of databases   Name    |  Owner   | Encoding  |  Collation  |    Ctype    |          Access Privileges          -----------+----------+-----------+-------------+-------------+------------------------------------- clocaledb | hlinnaka | SQL_ASCII | C           | C           |  englishdb | hlinnaka | UTF8      | en_GB.UTF8  | en_GB.UTF8  |  japanese  | hlinnaka | UTF8      | ja_JP.UTF8  | ja_JP.UTF8  |  korean    | hlinnaka | EUC_KR    | ko_KR.euckr | ko_KR.euckr |  postgres  | hlinnaka | UTF8      | fi_FI.UTF8  | fi_FI.UTF8  |  template0 | hlinnaka | UTF8      | fi_FI.UTF8  | fi_FI.UTF8  | {=c/hlinnaka,hlinnaka=CTc/hlinnaka} template1 | hlinnaka | UTF8      | fi_FI.UTF8  | fi_FI.UTF8  | {=c/hlinnaka,hlinnaka=CTc/hlinnaka}(7 rows)

22.3.3. Automatic Character Set Conversion Between Server and Client

PostgreSQL supports automatic character set conversion between server and client for certain character set combinations. The conversion information is stored in thepg_conversion system catalog.PostgreSQL comes with some predefined conversions, as shown inTable 22-2. You can create a new conversion using the SQL commandCREATE CONVERSION.

To enable automatic character set conversion, you have to tellPostgreSQL the character set (encoding) you would like to use in the client. There are several ways to accomplish this:

• Using the\encoding command inpsql.\encoding allows you to change client encoding on the fly. For example, to change the encoding toSJIS, type:

  \encoding SJIS

• libpq (Section 31.10) has functions to control the client encoding.

• UsingSET client_encoding TO. Setting the client encoding can be done with this SQL command:

  SET CLIENT_ENCODING TO 'value';

  Also you can use the standard SQL syntaxSET NAMES for this purpose:

  SET NAMES 'value';

  To query the current client encoding:

  SHOW client_encoding;

  To return to the default encoding:

  RESET client_encoding;

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

• Using the configuration variableclient_encoding. If theclient_encoding variable is set, that client encoding is automatically selected when a connection to the server is made. (This can subsequently be overridden using any of the other methods mentioned above.)

If the conversion of a particular character is not possible — suppose you choseEUC_JP for the server andLATIN1 for the client, and some Japanese characters are returned that do not have a representation inLATIN1 — an error is reported.

If the client character set is defined asSQL_ASCII, encoding conversion is disabled, regardless of the server's character set. Just as for the server, use ofSQL_ASCII is unwise unless you are working with all-ASCII data.

22.3.4. Further Reading

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