The catalog pg_collation
describes the available collations, which are essentially mappings from an SQL name to operating system locale categories. See Section 23.2 for more information.
Table 51.12. pg_collation
Columns
Name | Type | References | Description |
---|---|---|---|
Note that the unique key on this catalog is (collname
, collencoding
, collnamespace
) not just (collname
, collnamespace
). PostgreSQL generally ignores all collations that do not have collencoding
equal to either the current database's encoding or -1, and creation of new entries with the same name as an entry with collencoding
= -1 is forbidden. Therefore it is sufficient to use a qualified SQL name (schema
.name
) to identify a collation, even though this is not unique according to the catalog definition. The reason for defining the catalog this way is that initdb fills it in at cluster initialization time with entries for all locales available on the system, so it must be able to hold entries for all encodings that might ever be used in the cluster.
In the template0
database, it could be useful to create collations whose encoding does not match the database encoding, since they could match the encodings of databases later cloned from template0
. This would currently have to be done manually.
oid
oid
Row identifier (hidden attribute; must be explicitly selected)
collname
name
Collation name (unique per namespace and encoding)
collnamespace
oid
pg_namespace
.oid
The OID of the namespace that contains this collation
collowner
oid
pg_authid
.oid
Owner of the collation
collprovider
char
Provider of the collation: d
= database default, c
= libc, i
= icu
collencoding
int4
Encoding in which the collation is applicable, or -1 if it works for any encoding
collcollate
name
LC_COLLATE
for this collation object
collctype
name
LC_CTYPE
for this collation object
collversion
text
Provider-specific version of the collation. This is recorded when the collation is created and then checked when it is used, to detect changes in the collation definition that could lead to data corruption.