SQL & PL/SQL

Hi,

I am using lag function to display values like below:
order details date starttime
----------------- -------- --------------
main order 1 07/10/12 06:00am
line 1 07/10/12 06:21am
line 2 07/10/12 06:31am
main order 2 07/11/12 07:00am
line 1 07/11/12 07:01am
line 2 07/11/12 07:02am
the data displays correctly when i use lag function except that the line 1 details are never getting displayed ie first line under every order does not get displayed?
is using lag function in this case correct? Where is the mistake? Any help would be appreciated.

Thanks