Обсуждение: Inheritance clarification please

Greets,
    I'm trying to get my head around what the benefits to inheritance are.

    Is the data duplicated or just referenced in the parent table? If it's
duplicated then the database size and bloat are an issue for me.

    Another question I have is that say I have a parent table users and a child
table hobbies...one of my users exists only in the users table but now I
want to add his hobbies...is it possible to change him over to the hobbies
table without deleting him in the user table, then inserting him into the
hobbies table from scratch?

tom writes:

>     Is the data duplicated or just referenced in the parent table? If it's
> duplicated then the database size and bloat are an issue for me.

Just in the parent table.

>     Another question I have is that say I have a parent table users and a child
> table hobbies...one of my users exists only in the users table but now I
> want to add his hobbies...is it possible to change him over to the hobbies
> table without deleting him in the user table, then inserting him into the
> hobbies table from scratch?

No.  "Class promotion" is not a common operation in object oriented
systems.

--
Peter Eisentraut   peter_e@gmx.net   http://funkturm.homeip.net/~peter