Re: constraint question

ok im dumb - but this is the novice list -

references category(category_id) 

worked after Id done everything correct 
mwaples@optusnet.com.au wrote:
> 
> I have a table category with columns -
> category_id , main_id
> 
> I would like to check that the main_id value exists in category_id in
> any row of the table category.
> 
> Is it possible to have a foreign key referring to the current table ?
> Or should I be using a trigger to do it ?
> 
> I'm thinking I have to use a trigger to do it - but want to make sure.