title: make default value for a field to be current_timestamp + some interval
body: <p>i wanna make the default value of a field to be 30 days more than whatever the current timestamp is i tried a lot of stuff with dateadd() and addtime() but it always gave me an syntax error</p>
  <p><code> create table test (Id serial,name varchar(10),Date timestamp default dateadd(day,30,cuurent_timestamp));</code></p>
  <p>this might give a rough idea of what i'm trying to achieve.</p>