SELECT DISTINCT question

I got a problem with query:

select distinct (date), bytes from access_log;

which works but not as I expect. I thought this query will select
all rows with distinct values of 'date' column, but it get
distinct pairs 'date, bytes' . From documnetation I see

"DISTINCT will eliminate all duplicate rows from the selection.
DISTINCT ON column will eliminate all duplicates in the specified column;
this is equivalent to using GROUP BY column.
ALL will return all candidate rows, including duplicates."

discovery=> select distinct on date,bytes from access_log;
ERROR: parser: parse error at or near ","

Regards,

Oleg
_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83