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From: "David G. Johnston" <david.g.johnston@gmail.com>
Date: Sun, 30 Jun 2024 17:15:43 -0700
Message-ID: <CAKFQuwbOOQ20=Pb5j-k+Sws22H5W9tnj-vve4MC-GQ9RmmtTxA@mail.gmail.com>
Subject: Re: Should we document how column DEFAULT expressions work?
To: David Rowley <dgrowleyml@gmail.com>
Cc: Peter Eisentraut <peter@eisentraut.org>, Tom Lane <tgl@sss.pgh.pa.us>, 
	James Coleman <jtc331@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
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On Sun, Jun 30, 2024 at 4:55=E2=80=AFPM David Rowley <dgrowleyml@gmail.com>=
 wrote:

>
> I'd like to know what led someone down the path of doing something
> like DEFAULT 'now()'::timestamp in a CREATE TABLE. Could it be a
> faulty migration tool that created these and people copy them thinking
> it's a legitimate syntax?
>
>
My thought process on this used to be:  Provide a text string of the
expression that is then stored within the catalog and eval'd during
runtime.  If the only thing you are providing is a single literal and not
some compound expression it isn't that obvious that you are supposed to
provide an unquoted expression - which feels like it should be immediately
evaluated - versus something that is a constant.  Kinda like dynamic SQL.

David J.

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<div dir=3D"ltr"><div dir=3D"ltr"><div class=3D"gmail_default" style=3D"fon=
t-family:arial,helvetica,sans-serif"><span style=3D"font-family:Arial,Helve=
tica,sans-serif">On Sun, Jun 30, 2024 at 4:55=E2=80=AFPM David Rowley &lt;<=
a href=3D"mailto:dgrowleyml@gmail.com">dgrowleyml@gmail.com</a>&gt; wrote:<=
/span><br></div></div><div class=3D"gmail_quote"><blockquote class=3D"gmail=
_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204=
,204);padding-left:1ex"><br>
I&#39;d like to know what led someone down the path of doing something<br>
like DEFAULT &#39;now()&#39;::timestamp in a CREATE TABLE. Could it be a<br=
>
faulty migration tool that created these and people copy them thinking<br>
it&#39;s a legitimate syntax?<br><br></blockquote><div><br></div><div class=
=3D"gmail_default" style=3D"font-family:arial,helvetica,sans-serif">My thou=
ght process on this used=C2=A0to=C2=A0be:=C2=A0 Provide a text string of th=
e expression that is then stored within the catalog and eval&#39;d during r=
untime.=C2=A0 If the only thing you are providing is a single literal and n=
ot some compound expression it isn&#39;t that obvious that you are supposed=
 to provide an unquoted expression - which feels like it should be immediat=
ely evaluated - versus something that is a constant.=C2=A0 Kinda like dynam=
ic SQL.</div><div class=3D"gmail_default" style=3D"font-family:arial,helvet=
ica,sans-serif"><br></div><div class=3D"gmail_default" style=3D"font-family=
:arial,helvetica,sans-serif">David J.</div><div class=3D"gmail_default" sty=
le=3D"font-family:arial,helvetica,sans-serif"><br></div></div></div>

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