codice:
select 
case 
when valore between 1 and 2 then "1-2"
when valore between 3 and 4 then "3-4"
when valore between 5 and 9 then "5-9"
when valore between 10 and 16 then "10-16"
end
as fasce,
count(*) as quanti  
from tabella
group by fasce