Firebird - Tabelas sem Chave Primária (PK)

SELECT
   RDB$RELATION_NAME AS TABELA_SEM_PK
FROM RDB$RELATIONS
WHERE
   COALESCE(RDB$RELATION_TYPE,0) IN ( 0, 4, 5 ) AND
   ( RDB$SYSTEM_FLAG = 0 OR RDB$SYSTEM_FLAG IS NULL ) AND

   RDB$RELATION_NAME NOT IN (
      SELECT RDB$RELATION_NAME FROM RDB$RELATION_CONSTRAINTS WHERE RDB$CONSTRAINT_TYPE = 'PRIMARY KEY'
   )
ORDER BY RDB$RELATION_NAME