the best way to get the first record from each group

Hi,
Is there any better alternative to get the first record from each group?
"subno" is an integer, record with the smallest subno in each group is the
first record in the group.


select itemno, measureunit, extaxprice from itmt_purchase  where subno in (select min(subno)as subno  from
itmt_purchase group by itemno   order by itemno)  order by itemno, measureunit;
 



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