[SQL] Date of creation and of change

[Andreas Tille]

Hello,

could someone enlighten a fairly beginner how to define columns
of a table with the following features:

   CreateDate DEFAULT value should store current date and time
   ChangeDate DEFAULT value at creation as above and a Trigger
              function which stores data end time of any change
              to the data set

I hope someone has this quite usual feature handy or at least a
pointer where this is described.

Thank you very much

           Andreas.