Subject: Re: [PATCH] Generic type subscripting
To: Arthur Zakirov <a.zakirov@postgrespro.ru>
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Cc: Dmitry Dolgov <9erthalion6@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>,
 David Steele <david@pgmasters.net>,
 PostgreSQL-development <pgsql-hackers@postgresql.org>
From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Organization: 2ndQuadrant
Message-ID: <bb39cf19-744c-e320-3f3d-42dbe4af51bf@2ndquadrant.com>
Date: Wed, 20 Sep 2017 09:35:06 -0400
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On 9/20/17 04:12, Arthur Zakirov wrote:
> On Tue, Sep 19, 2017 at 09:01:57PM -0400, Peter Eisentraut wrote:
>> Would you mind posting a summary of how you go here?
> 
> There were several points here to me:
> - it is necessary to solve the dependency problem (it can be solved also by adding several oid fields to the pg_type)

A few oid or regproc fields in pg_type seem sensible.

> - users may want to add subscripting to their existing type, which already created in their database, or drop subscripting from existing type (it cannot be done by CREATE TYPE)

That's what ALTER TYPE is for.

> - other type related functionalities have their CREATE command and system catalog table. For example, CREATE CAST, CREATE TRANSFORM (this is a weakest point I think, mostly because of several casts and transforms can be defined to one type, and only one subscripting can be defined to one type).

The difference is that those create associations between two separate
objects (cast: type1 <-> type2, transform: type <-> language).  A
subscripting is just a property of a type.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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