table name :xyz coulumname is :submitdate datatype is : datetime

Initially submitdate by default is null

i updated the column for 100 orders to '02-02-2012 00.00.000'

update xys set submitdate='02-02-2012 00.00.000' where id in ('1','2'.........'100')

Now i want to revert back those 100 orders submitdate value to null .