Select
   TABS.RDB$RELATION_NAME as NOME_TABELA ,
   ( Select count(1) from RDB$RELATION_FIELDS CAMPS where CAMPS.RDB$RELATION_NAME = TABS.RDB$RELATION_NAME ) as NUM_CAMPOS
from RDB$RELATIONS TABS
where
   TABS.RDB$SYSTEM_FLAG=0
order by
   2 desc, 1