pg_collation
   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 | 
|---|---|---|---|
| oid | oid | Row identifier | |
| collname | name | Collation name (unique per namespace and encoding) | |
| collnamespace | oid |  | The OID of the namespace that contains this collation | 
| collowner | oid |  | Owner of the collation | 
| collprovider | char | Provider of the collation: d= database
       default,c= libc,i= icu | |
| collisdeterministic | bool | Is the collation deterministic? | |
| collencoding | int4 | Encoding in which the collation is applicable, or -1 if it works for any encoding | |
| collcollate | name | LC_COLLATEfor this collation object | |
| collctype | name | LC_CTYPEfor 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. | 
   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.