> - Is this correct for all db's or just Postgres?
All DBs, this is a property of the DB type mappings.
> - If so is it a good design pratice to define sql
> tables as allowing NULL and NOT NULL using Integer
> and int declarations on entity bean fields ( as
> opposed to doing this directly in SQL)
There is no meaningful value for a primitive int if NULL is present in the column, an Integer field can contain a null reference I guess.
> - Are there any performance or other issues
Performance different would be insignificant.