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'\" t
.\" Title: CREATE CONVERSION
.\" Author: The PostgreSQL Global Development Group
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\" Date: 2023
.\" Manual: PostgreSQL 15.5 Documentation
.\" Source: PostgreSQL 15.5
.\" Language: English
.\"
.TH "CREATE CONVERSION" "7" "2023" "PostgreSQL 15.5" "PostgreSQL 15.5 Documentation"
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.nh
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.SH "NAME"
CREATE_CONVERSION \- define a new encoding conversion
.SH "SYNOPSIS"
.sp
.nf
CREATE [ DEFAULT ] CONVERSION \fIname\fR
FOR \fIsource_encoding\fR TO \fIdest_encoding\fR FROM \fIfunction_name\fR
.fi
.SH "DESCRIPTION"
.PP
\fBCREATE CONVERSION\fR
defines a new conversion between two character set encodings\&.
.PP
Conversions that are marked
DEFAULT
can be used for automatic encoding conversion between client and server\&. To support that usage, two conversions, from encoding A to B
\fIand\fR
from encoding B to A, must be defined\&.
.PP
To be able to create a conversion, you must have
EXECUTE
privilege on the function and
CREATE
privilege on the destination schema\&.
.SH "PARAMETERS"
.PP
DEFAULT
.RS 4
The
DEFAULT
clause 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\&.
.RE
.PP
\fIname\fR
.RS 4
The name of the conversion\&. The conversion name can be schema\-qualified\&. If it is not, the conversion is defined in the current schema\&. The conversion name must be unique within a schema\&.
.RE
.PP
\fIsource_encoding\fR
.RS 4
The source encoding name\&.
.RE
.PP
\fIdest_encoding\fR
.RS 4
The destination encoding name\&.
.RE
.PP
\fIfunction_name\fR
.RS 4
The function used to perform the conversion\&. The function name can be schema\-qualified\&. If it is not, the function will be looked up in the path\&.
.sp
The function must have the following signature:
.sp
.if n \{\
.RS 4
.\}
.nf
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
boolean \-\- if true, don\*(Aqt throw an error if conversion fails
) RETURNS integer;
.fi
.if n \{\
.RE
.\}
.sp
The return value is the number of source bytes that were successfully converted\&. If the last argument is false, the function must throw an error on invalid input, and the return value is always equal to the source string length\&.
.RE
.SH "NOTES"
.PP
Neither the source nor the destination encoding can be
SQL_ASCII, as the server\*(Aqs behavior for cases involving the
SQL_ASCII
\(lqencoding\(rq
is hard\-wired\&.
.PP
Use
\fBDROP CONVERSION\fR
to remove user\-defined conversions\&.
.PP
The privileges required to create a conversion might be changed in a future release\&.
.SH "EXAMPLES"
.PP
To create a conversion from encoding
UTF8
to
LATIN1
using
\fBmyfunc\fR:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE CONVERSION myconv FOR \*(AqUTF8\*(Aq TO \*(AqLATIN1\*(Aq FROM myfunc;
.fi
.if n \{\
.RE
.\}
.SH "COMPATIBILITY"
.PP
\fBCREATE CONVERSION\fR
is a
PostgreSQL
extension\&. There is no
\fBCREATE CONVERSION\fR
statement in the SQL standard, but a
\fBCREATE TRANSLATION\fR
statement that is very similar in purpose and syntax\&.
.SH "SEE ALSO"
ALTER CONVERSION (\fBALTER_CONVERSION\fR(7)), CREATE FUNCTION (\fBCREATE_FUNCTION\fR(7)), DROP CONVERSION (\fBDROP_CONVERSION\fR(7))
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