select with group by problem

Hello,

could anyone tell me why the second select statement returns one row.

regards

Stephan

xtra=> select * from
warenkorb;                                                
cookie|datum|artnr|artnr1|artnr2|artikelname|farbe|groesse|menge|preis
------+-----+-----+------+------+-----------+-----+-------+-----+-----
(0 rows)

xtra=> SELECT artnr, artnr1, artnr2, artikelname, farbe, groesse, SUM(
menge ),preis FROM warenkorb WHERE cookie = 'asdfasdf' GROUP BY artnr, artnr1,
artnr2,artikelname, farbe, groesse, preis;
artnr|artnr1|artnr2|artikelname|farbe|groesse|sum|preis
-----+------+------+-----------+-----+-------+---+-----    |      |      |           |     |       |   |     
(1 row)