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'\" t
.\" Title: CREATE COLLATION
.\" Author: The PostgreSQL Global Development Group
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\" Date: 2024
.\" Manual: PostgreSQL 16.2 Documentation
.\" Source: PostgreSQL 16.2
.\" Language: English
.\"
.TH "CREATE COLLATION" "7" "2024" "PostgreSQL 16.2" "PostgreSQL 16.2 Documentation"
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.nh
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.\" * MAIN CONTENT STARTS HERE *
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.SH "NAME"
CREATE_COLLATION \- define a new collation
.SH "SYNOPSIS"
.sp
.nf
CREATE COLLATION [ IF NOT EXISTS ] \fIname\fR (
[ LOCALE = \fIlocale\fR, ]
[ LC_COLLATE = \fIlc_collate\fR, ]
[ LC_CTYPE = \fIlc_ctype\fR, ]
[ PROVIDER = \fIprovider\fR, ]
[ DETERMINISTIC = \fIboolean\fR, ]
[ RULES = \fIrules\fR, ]
[ VERSION = \fIversion\fR ]
)
CREATE COLLATION [ IF NOT EXISTS ] \fIname\fR FROM \fIexisting_collation\fR
.fi
.SH "DESCRIPTION"
.PP
\fBCREATE COLLATION\fR
defines a new collation using the specified operating system locale settings, or by copying an existing collation\&.
.PP
To be able to create a collation, you must have
CREATE
privilege on the destination schema\&.
.SH "PARAMETERS"
.PP
IF NOT EXISTS
.RS 4
Do not throw an error if a collation with the same name already exists\&. A notice is issued in this case\&. Note that there is no guarantee that the existing collation is anything like the one that would have been created\&.
.RE
.PP
\fIname\fR
.RS 4
The name of the collation\&. The collation name can be schema\-qualified\&. If it is not, the collation is defined in the current schema\&. The collation name must be unique within that schema\&. (The system catalogs can contain collations with the same name for other encodings, but these are ignored if the database encoding does not match\&.)
.RE
.PP
\fIlocale\fR
.RS 4
The locale name for this collation\&. See
Section\ \&24.2.2.3.1
and
Section\ \&24.2.2.3.2
for details\&.
.sp
If
\fIprovider\fR
is
libc, this is a shortcut for setting
LC_COLLATE
and
LC_CTYPE
at once\&. If you specify
\fIlocale\fR, you cannot specify either of those parameters\&.
.RE
.PP
\fIlc_collate\fR
.RS 4
If
\fIprovider\fR
is
libc, use the specified operating system locale for the
LC_COLLATE
locale category\&.
.RE
.PP
\fIlc_ctype\fR
.RS 4
If
\fIprovider\fR
is
libc, use the specified operating system locale for the
LC_CTYPE
locale category\&.
.RE
.PP
\fIprovider\fR
.RS 4
Specifies the provider to use for locale services associated with this collation\&. Possible values are
icu
(if the server was built with ICU support) or
libc\&.
libc
is the default\&. See
Section\ \&24.1.4
for details\&.
.RE
.PP
DETERMINISTIC
.RS 4
Specifies whether the collation should use deterministic comparisons\&. The default is true\&. A deterministic comparison considers strings that are not byte\-wise equal to be unequal even if they are considered logically equal by the comparison\&. PostgreSQL breaks ties using a byte\-wise comparison\&. Comparison that is not deterministic can make the collation be, say, case\- or accent\-insensitive\&. For that, you need to choose an appropriate
LC_COLLATE
setting
\fIand\fR
set the collation to not deterministic here\&.
.sp
Nondeterministic collations are only supported with the ICU provider\&.
.RE
.PP
\fIrules\fR
.RS 4
Specifies additional collation rules to customize the behavior of the collation\&. This is supported for ICU only\&. See
Section\ \&24.2.3.4
for details\&.
.RE
.PP
\fIversion\fR
.RS 4
Specifies the version string to store with the collation\&. Normally, this should be omitted, which will cause the version to be computed from the actual version of the collation as provided by the operating system\&. This option is intended to be used by
\fBpg_upgrade\fR
for copying the version from an existing installation\&.
.sp
See also
ALTER COLLATION (\fBALTER_COLLATION\fR(7))
for how to handle collation version mismatches\&.
.RE
.PP
\fIexisting_collation\fR
.RS 4
The name of an existing collation to copy\&. The new collation will have the same properties as the existing one, but it will be an independent object\&.
.RE
.SH "NOTES"
.PP
\fBCREATE COLLATION\fR
takes a
SHARE ROW EXCLUSIVE
lock, which is self\-conflicting, on the
pg_collation
system catalog, so only one
\fBCREATE COLLATION\fR
command can run at a time\&.
.PP
Use
\fBDROP COLLATION\fR
to remove user\-defined collations\&.
.PP
See
Section\ \&24.2.2.3
for more information on how to create collations\&.
.PP
When using the
libc
collation provider, the locale must be applicable to the current database encoding\&. See
CREATE DATABASE (\fBCREATE_DATABASE\fR(7))
for the precise rules\&.
.SH "EXAMPLES"
.PP
To create a collation from the operating system locale
fr_FR\&.utf8
(assuming the current database encoding is
UTF8):
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE COLLATION french (locale = \*(Aqfr_FR\&.utf8\*(Aq);
.fi
.if n \{\
.RE
.\}
.PP
To create a collation using the ICU provider using German phone book sort order:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE COLLATION german_phonebook (provider = icu, locale = \*(Aqde\-u\-co\-phonebk\*(Aq);
.fi
.if n \{\
.RE
.\}
.PP
To create a collation using the ICU provider, based on the root ICU locale, with custom rules:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE COLLATION custom (provider = icu, locale = \*(Aqund\*(Aq, rules = \*(Aq&V << w <<< W\*(Aq);
.fi
.if n \{\
.RE
.\}
.sp
See
Section\ \&24.2.3.4
for further details and examples on the rules syntax\&.
.PP
To create a collation from an existing collation:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE COLLATION german FROM "de_DE";
.fi
.if n \{\
.RE
.\}
.sp
This can be convenient to be able to use operating\-system\-independent collation names in applications\&.
.SH "COMPATIBILITY"
.PP
There is a
\fBCREATE COLLATION\fR
statement in the SQL standard, but it is limited to copying an existing collation\&. The syntax to create a new collation is a
PostgreSQL
extension\&.
.SH "SEE ALSO"
ALTER COLLATION (\fBALTER_COLLATION\fR(7)), DROP COLLATION (\fBDROP_COLLATION\fR(7))
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