To: Reza Shanbehbazari Mirzaei <mirzaei@stud.ntnu.no>
Cc: pgsql-sql@postgresql.org
Subject: Re: User defined types 
In-reply-to: <Pine.LNX.4.58.0411201729220.32082@jaguar.stud.ntnu.no> 
References: <Pine.LNX.4.58.0411201729220.32082@jaguar.stud.ntnu.no>
Comments: In-reply-to Reza Shanbehbazari Mirzaei <mirzaei@stud.ntnu.no>
	message dated "Sat, 20 Nov 2004 17:35:33 +0100"
Date: Thu, 25 Nov 2004 13:29:42 -0500
Message-ID: <1114.1101407382@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Reza Shanbehbazari Mirzaei <mirzaei@stud.ntnu.no> writes:
>   I have a user define type called VALID_TIME. It is declared as follows:

>   CREATE TYPE VALID_TIME AS (t_s TIMESTAMP, t_e TIMESTAMP);

>   Once I have used this in a table declaration, is it possible to extract
> parts of it, for example to only read t_s or t_e? If so, how do I do this?

8.0 supports using composite types as table columns, but prior versions
don't really.  In 8.0 you'd do something like

	create table myt (vt valid_time);

	select (vt).t_s from myt;
or
	select (myt.vt).t_s from myt;

The parentheses are essential --- without them, you'd have for instance

	select vt.t_s from myt;

which looks like a reference to field t_s of table vt, not what you
want.

You can hack around the problem in earlier versions by creating helper
functions, eg

	select get_t_s(vt) from myt;

but it's ugly enough to make one wonder why bother with a composite type.

			regards, tom lane