select floor(regno/100) "groupby", min(regno),max(regno),min(name),max(name) 
from registrations 
group by `groupby`;

##</code><code>##

set @rownum := 0;
select floor(@rownum  := @rownum + 0.01) "set_num", min(lname),max(lname) 
from (select * from registrants order by lname) reg 
group by "set_num";