codice:
select * from 
(select max(`data`) as `data` from tabella
group by azienda) as tab1
left join tabella as tab2 on tab1.`data` = tab2.`data`
order by tab1.`data` desc
ovviamente il campo data dovrà essere in formato date (AAAA-MM-GG) e non varchar(GG/MM/AAAA).