Re: postgresql table inheritance

On Fri, Nov 30, 2007 at 09:42:53PM +0800, Lincoln Yeoh wrote:
> Found this post on Slashdot which I found interesting, any comments?

I think this person is slightly confused.

> Table inheritence doesn't even make sense. Tables are analogous to
> relations.
> All relations are the same type, the relation type (think "set" or "array"
> to
> make it easier). How can one value of a type (one table) be a subtype of
> another value (another table)?

Easy, by having the columns of one table be a subset of the columns or
another table. Perhaps someone should point out an example, like a
table with "people" and subtables "employees" and "customers". The
subtables share the columns of the parent tables. This is nothing that
any OO language doesn't do.

> The correct way to store types and subtypes in the database is to store them
> in the columns. In other words, choose attribute VALUES from a TYPE SYSTEM.
> Nothing else in the relational model needs to be changed. Something like
> this, in hypothetical SQL-like language:

His example is a little wierd, but it is possible:

test=# create type foo as (a text, b text);
CREATE TYPE
test=# create table test( id  int4, vals foo );
CREATE TABLE
test=# insert into test values ( 4, ROW('a', 'b'));
INSERT 0 1
test=# select * from test;
 id | vals
----+-------
  4 | (a,b)
(1 row)

The syntax is different but the ideas are there...

Have a nice day,
--
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Those who make peaceful revolution impossible will make violent revolution inevitable.
>  -- John F Kennedy