CONVERT

Syntax

Description of the illustration convert.gif

Purpose

CONVERT converts a character string from one character set to another.

The char argument is the value to be converted. It can be any of the datatypes CHAR, VARCHAR2, NCHAR, NVARCHAR2, CLOB, or NCLOB.
The dest_char_set argument is the name of the character set to which char is converted.
The source_char_set argument is the name of the character set in which char is stored in the database. The default value is the database character set.

The return value for CHAR and VARCHAR2 is VARCHAR2. For NCHAR and NVARCHAR2, it is NVARCHAR2. For CLOB, it is CLOB, and for NCLOB, it is NCLOB.

Both the destination and source character set arguments can be either literals or columns containing the name of the character set.

For complete correspondence in character conversion, it is essential that the destination character set contains a representation of all the characters defined in the source character set. Where a character does not exist in the destination character set, a replacement character appears. Replacement characters can be defined as part of a character set definition.

Note:

Oracle discourages the use of the CONVERT function in the current Oracle Database release. The return value of CONVERT has a character datatype, so it should be either in the database character set or in the national character set, depending on the datatype. Any dest_char_set that is not one of these two character sets is unsupported. The char argument and the source_char_set have the same requirements. Therefore, the only practical use of the function is to correct data that has been stored in a wrong character set.

Values that are in neither the database nor the national character set should be processed and stored as RAW or BLOB. Procedures in the PL/SQL packages UTL_RAW and UTL_I18N—for example, UTL_RAW.CONVERT—allow limited processing of such values. Procedures accepting RAW argument in the packages UTL_FILE, UTL_TCP, UTL_HTTP, and UTL_SMTP can be used to output the processed data.

Examples

The following example illustrates character set conversion by converting a Latin-1 string to ASCII. The result is the same as importing the same string from a WE8ISO8859P1 database to a US7ASCII database.

SELECT CONVERT('Ä Ê Í Ó Ø A B C D E ', 'US7ASCII', 'WE8ISO8859P1') 
   FROM DUAL; 

CONVERT('ÄÊÍÓØABCDE' 
--------------------- 
A E I ? ? A B C D E ?

Common character sets include:

US7ASCII: US 7-bit ASCII character set
WE8ISO8859P1: ISO 8859-1 West European 8-bit character set
EE8MSWIN1250: Microsoft Windows East European Code Page 1250
WE8MSWIN1252: Microsoft Windows West European Code Page 1252
WE8EBCDIC1047: IBM West European EBCDIC Code Page 1047
JA16SJISTILDE: Japanese Shift-JIS Character Set, compatible with MS Code Page 932
ZHT16MSWIN950: Microsoft Windows Traditional Chinese Code Page 950
UTF8: Unicode 3.0 Universal character set CESU-8 encoding form
AL32UTF8: Unicode 5.0 Universal character set UTF-8 encoding form

You can query the V$NLS_VALID_VALUES view to get a listing of valid character sets, as follows:

SELECT * FROM V$NLS_VALID_VALUES WHERE parameter = 'CHARACTERSET'