sql: add pg_encoding_to_char()

[BramGruneir]

pg_encoding_to_char() translates the value in the pg_database.encoding column into a string that represents the encoding. See https://www.postgresql.org/docs/10/static/catalog-pg-database.html

Since CockroachDB uses UTF-8 everywhere this should be straightforward, but the function should assert that its argument is the value presented in pg_database.encoding.

PGAdmin issues the following query:

SELECT db.oid AS did,
       db.datname AS name,
       db.dattablespace AS spcoid,
       spcname,
       datallowconn,
       pg_encoding_to_char(encoding) AS encoding,
       pg_get_userbyid(datdba) AS datowner,
       datcollate,
       datctype,
       datconnlimit,
       has_database_privilege(db.oid, 'CREATE') AS cancreate,
       current_setting('default_tablespace') AS default_tablespace,
       descr.description AS comments,
       db.datistemplate AS is_template,
       (
         SELECT array_to_string(ARRAY (
          SELECT array_to_string(defaclacl::TEXT[], ', ')
          FROM pg_default_acl
          WHERE (defaclobjtype = 'r')
            AND (defaclnamespace = 0::OID)
         ), ', ')
        ) AS tblacl,
        (
          SELECT array_to_string(ARRAY (
            SELECT array_to_string(defaclacl::TEXT[], ', ')
            FROM pg_default_acl
            WHERE (defaclobjtype = 'S')
              AND (defaclnamespace = 0::OID)
          ), ', ')
        ) AS seqacl,
        (
          SELECT array_to_string(ARRAY (
            SELECT array_to_string(defaclacl::TEXT[], ', ')
            FROM pg_default_acl
            WHERE (defaclobjtype = 'f')
              AND (defaclnamespace = 0::OID)
          ), ', ')
        ) AS funcacl,
        (
          SELECT array_to_string(ARRAY (
            SELECT array_to_string(defaclacl::TEXT[], ', ')
            FROM pg_default_acl
            WHERE (defaclobjtype = 'T')
              AND (defaclnamespace = 0::OID)
          ), ', ')
        ) AS typeacl,
        (
          SELECT array_agg((provider || '=') || label)
          FROM pg_shseclabel AS sl1
          WHERE sl1.objoid = db.oid
        ) AS seclabels,
        array_to_string(datacl::TEXT[], ', ') AS acl
FROM pg_database AS db
LEFT JOIN pg_tablespace AS ta
  ON db.dattablespace = ta.oid
LEFT JOIN pg_shdescription AS descr
  ON ((db.oid = descr.objoid) AND (descr.classoid = 'pg_database'::REGCLASS))
WHERE db.oid > NULL::OID
ORDER BY datname

Details can be found here: https://www.postgresql.org/docs/current/static/libpq-control.html

[jordanlewis]

This was added a while back, and the pasted query works now.