CREATE CONVERSION

Defines a new encoding conversion.

Synopsis

CREATE [DEFAULT] CONVERSION <name>
     FOR <source_encoding> TO <dest_encoding> FROM <function_name>

Description

CREATE CONVERSION defines a new conversion between character set encodings. Also, conversions that are marked DEFAULT can be used for automatic encoding conversion between client and server. For this purpose, two conversions, from encoding A to B and from encoding B to A, must be defined.

To create a conversion, you must have EXECUTE privilege on the function and CREATE privilege on the destination schema.

Parameters

DEFAULT

Indicates that this conversion is the default for this particular source to destination encoding. There should be only one default encoding in a schema for the encoding pair.

name

The name of the conversion. The conversion name may be schema-qualified. If it is not, the conversion is defined in the current schema. The conversion name must be unique within a schema.

source_encoding

The source encoding name.

dest_encoding

The destination encoding name.

function_name

The function used to perform the conversion. The function name may be schema-qualified. If it is not, the function will be looked up in the path. The function must have the following signature:

conv_proc(
integer,  -- source encoding ID
integer,  -- destination encoding ID
cstring,  -- source string (null terminated C string)
internal, -- destination (fill with a null terminated C string)
integer   -- source string length
) RETURNS void;

Notes

Use DROP CONVERSION to remove a user-defined conversion.

The privileges required to create a conversion might change in a feature release.

Note that in this release of Greenplum Database, user-defined functions used in a user-defined conversion must be defined as IMMUTABLE. Any compiled code (shared library files) for custom functions must be placed in the same location on every host in your Greenplum Database array (coordinator and all segments). This location must also be in the LD_LIBRARY_PATH so that the server can locate the files.

Examples

To create a conversion from encoding UTF8 to LATIN1 using myfunc:

CREATE CONVERSION myconv FOR 'UTF8' TO 'LATIN1' FROM myfunc;

Compatibility

CREATE CONVERSION is a Greenplum Database extension. There is no CREATE CONVERSION statement in the SQL standard, but there is a CREATE TRANSLATION statement that is very similar in purpose and syntax.