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References: <D78EPGDRGTYO.1C8SB09QLCOHE@runxiyu.org>
In-Reply-To: <D78EPGDRGTYO.1C8SB09QLCOHE@runxiyu.org>
From: Greg Sabino Mullane <htamfids@gmail.com>
Date: Wed, 22 Jan 2025 10:11:26 -0500
Message-ID: <CAKAnmmLd9okDxM79MMomOvjLECm3zZfqbeUGY0RORCPwzTSqQw@mail.gmail.com>
Subject: Re: Automatic deletion of orphaned rows
To: Runxi Yu <me@runxiyu.org>
Cc: pgsql-general@lists.postgresql.org
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On Wed, Jan 22, 2025 at 2:00=E2=80=AFAM Runxi Yu <me@runxiyu.org> wrote:

> I therefore propose a feature, to be able to specify in a table schema
> that a row should be deleted if orphaned.
>

I think you mean "childless" rows, as "orphaned" has a different meaning
traditionally.

When and how would this deletion take place? And why not just run the
delete yourself?
It would help to show us exactly the behavior you want. Here's some sample
tables we
can use:

create table parent( id int primary key );

create table kid( refid int references parent(id) );

insert into parent values (1),(2),(3);

insert into kid values (1);

-- remove any rows non-referenced rows (aka childless)
delete from parent where not exists (select 1 from kid where refid=3Dparent=
.id
);

select * from parent;
 id
----
  1

Cheers,
Greg

--
Crunchy Data - https://www.crunchydata.com
Enterprise Postgres Software Products & Tech Support

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<div dir=3D"ltr"><div dir=3D"ltr"><div dir=3D"ltr">On Wed, Jan 22, 2025 at =
2:00=E2=80=AFAM Runxi Yu &lt;<a href=3D"mailto:me@runxiyu.org" target=3D"_b=
lank">me@runxiyu.org</a>&gt; wrote:</div><div class=3D"gmail_quote"><blockq=
uote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1p=
x solid rgb(204,204,204);padding-left:1ex">I therefore propose a feature, t=
o be able to specify in a table schema that a row should be deleted if orph=
aned.<br></blockquote><div><br></div><div>I think you mean &quot;childless&=
quot; rows, as &quot;orphaned&quot; has a different meaning traditionally.<=
/div><div><br></div><div>When and how would this deletion take place? And w=
hy not just run the delete yourself?<br>It would help to show us exactly th=
e behavior you want. Here&#39;s some sample tables we<br>can use:<br><br>cr=
eate table parent( id int primary key );<br><br>create table kid( refid int=
 references parent(id) );<br><br>insert into parent values (1),(2),(3);<br>=
<br>insert into kid values (1);<br><br>-- remove any rows non-referenced ro=
ws (aka childless)<br>delete from parent where not exists (select 1 from ki=
d where refid=3D<a href=3D"http://parent.id" target=3D"_blank">parent.id</a=
>);<br><br>select * from parent;<br>=C2=A0id<br>----<br>=C2=A0 1</div><div>=
<br></div><div>Cheers,</div><div>Greg</div><div><br></div><div>--<br>Crunch=
y Data - <a href=3D"https://www.crunchydata.com">https://www.crunchydata.co=
m</a><br>Enterprise Postgres Software Products &amp; Tech Support<br></div>=
<div><br></div></div></div>
</div>

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