On Tue, 2005-05-03 at 17:31, Roderick A. Anderson wrote:
> I am trying to come up with a method to have a default value for a
> column based on a function and other columns. I'm hoping ( well not too
> much ) that what I figure out here will apply to MS SQL Server as I am
> stuck using it unless I can prove there ain't no way it's going to
> happen. ( Now that the embarrassment of being stuck using SQL Server is
> out of the way. )
>
> I'd like to populate a column with the md5 of ColA || ':' || ColB || ':'
> || ColC. A search of the archives ( with the terms I was using )
> didn't turn up anything useful.
>
> Would this be a function or a trigger?
This will be an after trigger function (everything's a function! woot!
hehe. seriously though, all triggers are functions, but not all
functions are triggers, in postgresql land).
Basically, you'll need an after trigger that updates the md5 field with
that cola/b/c bit you've got up there. Not much to it really.
One of the examples on this page ought to help:
http://www.postgresql.org/docs/8.0/static/plpgsql-trigger.html