SELECT
  d.datname AS"Name",
  pg_catalog.pg_get_userbyid(d.datdba) AS"Owner",
  pg_catalog.pg_encoding_to_char(d.encoding) AS"Encoding",
  d.datcollate AS"Collate",
  d.datctype AS"Ctype",
  pg_catalog.array_to_string(d.datacl, E'
') AS"Access privileges",
  CASE WHEN pg_catalog.has_database_privilege(d.datname, 'CONNECT')
    THEN pg_catalog.pg_size_pretty(pg_catalog.pg_database_size(d.datname))
    ELSE 'No Access'
  END AS"Size",
  t.spcname AS"Tablespace",
  pg_catalog.shobj_description(d.oid, 'pg_database') AS"Description"
FROM
  pg_catalog.pg_database d
JOIN
  pg_catalog.pg_tablespace t ON d.dattablespace = t.oid
ORDER BY 1;

CREATE OR REPLACE FUNCTION databases_schemas_size
  () RETURNS setof RECORD
AS
  $body$

  DECLARE

    connection_info CHARACTER VARYING;
    i RECORD;
    r RECORD;

  BEGIN

    FOR r IN SELECT CAST(datname AS CHARACTER VARYING) FROM  pg_database  WHERE  datistemplate = FALSE LOOP

    SELECT format ('dbname=%s user=%s password=%s', r.datname, 'YOUR_ALLOWED_USERNAME', 'PASSWORD') INTO   connection_info;

    perform dblink_connect(connection_info);
    FOR i IN SELECT r.datname, *
    FROM   dblink('SELECT nspname , pg_size_pretty(sum(pg_relation_size(C.oid))) AS size FROM pg_class C LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace) WHERE nspname NOT IN (''pg_catalog'', ''information_schema'') group by nspname')
    AS t(schema_name CHARACTER VARYING, schema_size text)

    LOOP
    RETURN NEXT i;
    END LOOP;

  perform dblink_disconnect();
END LOOP;

RETURN;

END;
$body$ LANGUAGE plpgsql volatile cost 100;


SELECT * FROM  databases_schemas_size()
AS (datname CHARACTER VARYING, schema_name CHARACTER VARYING, schema_size text);