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Date: Wed, 6 Sep 2023 13:02:50 +0200
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Subject: Re: information_schema and not-null constraints
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To: Alvaro Herrera <alvherre@alvh.no-ip.org>,
 Pg Hackers <pgsql-hackers@lists.postgresql.org>
References: <202309051624.hrzj5uy3dmg3@alvherre.pgsql>
From: Peter Eisentraut <peter@eisentraut.org>
In-Reply-To: <202309051624.hrzj5uy3dmg3@alvherre.pgsql>
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On 05.09.23 18:24, Alvaro Herrera wrote:
> On 2023-Sep-05, Peter Eisentraut wrote:
> 
>> The following information schema views are affected by the not-null
>> constraint catalog entries:
>>
>> 1. CHECK_CONSTRAINTS
>> 2. CONSTRAINT_COLUMN_USAGE
>> 3. DOMAIN_CONSTRAINTS
>> 4. TABLE_CONSTRAINTS
>>
>> Note that 1 and 3 also contain domain constraints.
> 
> After looking at what happens for domain constraints in older versions
> (I tested 15, but I suppose this applies everywhere), I notice that we
> don't seem to handle them anywhere that I can see.  My quick exercise is
> just
> 
> create domain nnint as int not null;
> create table foo (a nnint);
> 
> and then verify that this constraint shows nowhere -- it's not in
> DOMAIN_CONSTRAINTS for starters, which is I think the most obvious place.
> And nothing is shown in CHECK_CONSTRAINTS nor TABLE_CONSTRAINTS either.
> 
> This did ever work in the past?  I tested with 9.3 and didn't see
> anything there either.

No, this was never implemented.  (As I wrote in my other message on the 
other thread, arguably a bit buggy.)  We could fix this separately, 
unless we are going to implement catalogued domain not-null constraints 
soon.