From: "Wetmore, Matthew (CTR)" <Matthew.Wetmore@express-scripts.com>
To: Tom Lane <tgl@sss.pgh.pa.us>,
        "David G. Johnston"
	<david.g.johnston@gmail.com>
CC: Ilya Kosmodemiansky <ik@dataegret.com>,
        "pgsql-admin@lists.postgresql.org"
	<pgsql-admin@lists.postgresql.org>
Thread-Topic: [EXTERNAL] Re: GENERATE AS
Thread-Index: AdmlQrLyTyHk5PZ/Rt+vdgjgyKHjnQAJNXgAAABsLwAAAbq3gAAHF9UA
Date: Thu, 22 Jun 2023 22:00:47 +0000
Message-ID: <754d7cd591b74c8585f6efb0f4aef81a@express-scripts.com>
References: <7c48174f8ce449af8f3e875bdeca7150@express-scripts.com>
 <D598E4B1-1B40-4B55-89A2-9296CDD2985D@dataegret.com>
 <CAKFQuwbJcON2=Ky9rDNJdUGa8iuu6nYnPnRa_jr85iRkCokKww@mail.gmail.com>
 <4108564.1687468505@sss.pgh.pa.us>
In-Reply-To: <4108564.1687468505@sss.pgh.pa.us>
Accept-Language: en-US
Content-Language: en-US
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
Subject: GENERATE AS
Archived-At: 
 <https://www.postgresql.org/message-id/754d7cd591b74c8585f6efb0f4aef81a%40express-scripts.com>
Precedence: bulk

I got his working.

I understand everyone's great suggestions on functions and views, that's ho=
w I would have done this, but my requirement was very specific to my org.

This stemmed from a re-architecture  from MSSQL, and had to stay as is for =
MainFrame (I tried to get to change)

Basically, you just can't use the time functions(), in the GENERATE you hav=
e to create a separate column with default time that in my case (isn't used=
 by the other system, but gets defaulted on INSERT.)

Wonky, yes, but it will work for my specific need.  (I have whitewashed the=
 specific need for security, so if this seems simplified, it is.)

Thanks for all the replies!


ALTER TABLE matt
	add column matt_time timestamp without time zone default current_timestamp
=09
ALTER TABLE matt
	add column matt_time2 timestamp without time zone default current_timestam=
p=20

ALTER TABLE matt
	ADD column matt_minute NUMERIC GENERATED ALWAYS AS ((EXTRACT(MINUTE FROM m=
att_time))::numeric -(extract(MINUTE FROM matt_time2))::numeric) stored
=09
ALTER TABLE matt
	ADD column matt_hour NUMERIC GENERATED ALWAYS AS ((EXTRACT(HOUR FROM matt_=
time))::numeric -(extract(HOUR FROM matt_time2))::numeric) stored
=09
select * from auto_auth.matt

"matt_time"			"matt_time2"					"matt_hour"	"matt_minute"
"2023-06-22 17:30:53.33997"	"2023-06-22 17:36:27.356768"			0		-6


-----Original Message-----
From: Tom Lane <tgl@sss.pgh.pa.us>=20
Sent: Thursday, June 22, 2023 2:15 PM
To: David G. Johnston <david.g.johnston@gmail.com>
Cc: Ilya Kosmodemiansky <ik@dataegret.com>; Wetmore, Matthew (CTR) <Matthew=
.Wetmore@express-scripts.com>; pgsql-admin@lists.postgresql.org
Subject: [EXTERNAL] Re: GENERATE AS

"David G. Johnston" <david.g.johnston@gmail.com> writes:
> The problem here is not timezone related - it is more fundamental in=20
> that the stored data does not change but the expression, as time=20
> progresses, is going to give different values and thus make what is store=
d incorrect.

Right --- current_timestamp in a generation expression makes no sense.
(There's also an issue about whether the surrounding calculation is timezon=
e-dependent, but that could be fixed up.  Depending on current time cannot =
be.)

You could create a view in which this value is an extra computed column, bu=
t you can't do it as a stored generated column.

			regards, tom lane