generated dates from record dates - suggestions

Hi folks.

I've got a table with three dates which are populated from an external source.
I then want to have a view with two calculated dates in it, e.g.

if date_1 is null and date_2 is null then date_a=NULL
if date_1 is not null and date 2 is null then date_a=date_1+'90 days'
if date_1 > date3 rhen date_b=date1 else date_b=date2
etc.

What's the best way to do this?

I know it's a quite open question but I'm interested to hear different 
responses


-- 
Gary Stainburn
Group I.T. Manager
Ringways Garages
http://www.ringways.co.uk