Обсуждение: Inheritance

Hi,

I'm just wondering, what real benefit does inheritance have?  When i
create two tables, one inherited from the other,
does that mean i have two tables with same duplicate data or actually
they are joined in the back end?


Thank you for any input regarding this matter.

Hasnul

Hasnul Fadhly bin Hasan <hasnulfadhly.h@mimos.my> writes:
> I'm just wondering, what real benefit does inheritance have?  When i
> create two tables, one inherited from the other,
> does that mean i have two tables with same duplicate data or actually
> they are joined in the back end?

It's more like an implicit UNION ALL.  There's no duplication, but when
you specify a SELECT/UPDATE/DELETE over the parent table, the child
table is implicitly processed as well.

            regards, tom lane

When will the function inheritence be futher development? That Primary keys
work wil on both parent and child table.

Now a use one table and several table with the same foreign keys to that
table. And a function have to do two insert of update actions.

----- Original Message -----
From: "Tom Lane" <tgl@sss.pgh.pa.us>
To: "Hasnul Fadhly bin Hasan" <hasnulfadhly.h@mimos.my>
Cc: <pgsql-novice@postgresql.org>
Sent: Tuesday, December 21, 2004 4:45
Subject: Re: [NOVICE] Inheritance


> Hasnul Fadhly bin Hasan <hasnulfadhly.h@mimos.my> writes:
> > I'm just wondering, what real benefit does inheritance have?  When i
> > create two tables, one inherited from the other,
> > does that mean i have two tables with same duplicate data or actually
> > they are joined in the back end?
>
> It's more like an implicit UNION ALL.  There's no duplication, but when
> you specify a SELECT/UPDATE/DELETE over the parent table, the child
> table is implicitly processed as well.
>
> regards, tom lane
>
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On Tue, Dec 21, 2004 at 09:27:05 +0100,
  Tjibbe Rijpma <t.b.rijpma@student.tudelft.nl> wrote:
> When will the function inheritence be futher development? That Primary keys
> work wil on both parent and child table.

When someone does the work. This has been an open issue for a long time
and it doesn't seem to be a high priority for anyone.

> Now a use one table and several table with the same foreign keys to that
> table. And a function have to do two insert of update actions.

One reason that it probably isn't a high priority is you can do a lot of
the same stuff using views instead of inheritence.