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Re: [GENERAL] postgresql table inheritance
Date: Fri Nov 30 2007 - 09:20:57 EST
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(at)svana.org> http://svana.org/kleptog/Received on Fri Nov 30 09:22:16 2007
> Those who make peaceful revolution impossible will make violent revolution inevitable.
> -- John F Kennedy
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