Subject: Re: [HACKERS] proposal: schema variables
To: Pavel Stehule <pavel.stehule@gmail.com>,
 Robert Haas <robertmhaas@gmail.com>
References: 
 <CAFj8pRDY+m9OOxfO10R7J0PAkCCauM-TweaTrdsrsLGMb1VbEQ@mail.gmail.com>
 <20180417141410.GA7917@zakirov.localdomain>
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Cc: Arthur Zakirov <a.zakirov@postgrespro.ru>,
 PostgreSQL Hackers <pgsql-hackers@postgresql.org>
From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
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Message-ID: <1f204fb8-afe6-006d-853b-4da05b416840@2ndquadrant.com>
Date: Mon, 30 Apr 2018 21:56:45 -0400
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On 4/20/18 13:45, Pavel Stehule wrote:
>     I dunno, it seems awfully different to me.  There's only one "column",
>     right?  What code is really shared here?  Are constraints and triggers
>     even desirable feature for variables?  What would be the use case?
> 
> 
> The schema variable can hold composite value. The patch allows to use
> any composite type or adhoc composite values
> 
> DECLARE x AS compositetype;
> DECLARE x AS (a int, b int, c int);

I'm not sure that this anonymous composite type thing is such a good
idea.  Such a variable will then be incompatible with anything else,
because it's of a different type.

In any case, I find that a weak argument for storing this in pg_class.
You could just as well create these pg_class entries implicitly and link
them from "pg_variable", same as composite types have a main entry in
pg_type and additional stuff in pg_class.

>     I think stuffing this into pg_class is pretty strange.
> 
> It will be if variable is just scalar value without any possibilities.
> But then there is only low benefit
> 
> The access rights implementation is shared with other from pg_class too.

In DB2, the privileges for variables are named READ and WRITE.  That
would make more sense to me than reusing the privilege names for tables.

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