PostgreSQL Tables Without PKs

WITH relpub AS (
  SELECT  r.oid
      ,   r.relname
  FROM    pg_class r
          INNER JOIN pg_namespace n ON r.relnamespace = n.oid AND r.relkind = 'r' AND n.nspname = 'public'
),
pk AS (
  SELECT  r.oid
  FROM    relpub r
          INNER JOIN pg_index i ON r.oid = i.indrelid AND i.indisprimary
)
SELECT  r.relname
FROM    relpub r
WHERE   NOT EXISTS (
          SELECT  oid
          FROM    pk
          WHERE   oid = r.oid
        );