23.3. Character Set Support

Table 23.1 shows the character sets available for use in PostgreSQL .

Not all client API s support all the listed character sets. For example, the PostgreSQL JDBC driver does not support MULE_INTERNAL , LATIN6 , LATIN8 , and LATIN10 .

The SQL_ASCII setting behaves considerably differently from the other settings. When the server character set is SQL_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 is SQL_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 the SQL_ASCII setting because PostgreSQL will be unable to help you by converting or validating non-ASCII characters.

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

initdb -E EUC_JP

sets the default character set to EUC_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 named korean that uses the character set EUC_KR , and locale ko_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 the template0 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 see Section 22.3 .

The encoding for a database is stored in the system catalog pg_database . You can see it by using the psql -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)

PostgreSQL supports automatic character set conversion between server and client for certain character set combinations. The conversion information is stored in the pg_conversion system catalog. PostgreSQL comes with some predefined conversions, as shown in Table 23.2 . You can create a new conversion using the SQL command CREATE CONVERSION .

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

If the conversion of a particular character is not possible - suppose you chose EUC_JP for the server and LATIN1 for the client, and some Japanese characters are returned that do not have a representation in LATIN1 - an error is reported.

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

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