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. The 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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