sql - Partially distinct select

I have a table with fields utm and tracking_id. There may be many tracking_ids for each utm.
So I need to select distinct utm and any one tracking id for each utm (let`s say thefirst one).

For example, we got the table:

utm   | tracking_id
-------------------
ddff  |      1
ddff  |      2
llzz  |      3
ddff  |      4
ohoh  |      5
ohoh  |      6

And as an output i want to get:

utm   | tracking_id
-------------------
ddff  |      1
llzz  |      3
ohoh  |      5

I use PostgreSQL 9.1.
Is there a way to do it with SQL?

Answer

if you have only one column, than simple aggregate is what you want, go with Clodoaldo Neto's advice.
If you have more than one columns, you can use dictinst on syntax:

select distinct on(utm)
    utm, tracking_id, column1, column2, ...
from t
order by utm, tracking_id

sql fiddle demo