Message-ID: <642a6ec8-4ec3-4f2a-b39a-6855237a34c1@a-kretschmer.de>
Date: Tue, 10 Sep 2024 17:28:15 +0200
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Subject: Re: Removing duplicate rows in table
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To: pgsql-general@lists.postgresql.org
References: <e4688faf-de51-93ef-2db-f2acacbd658@appl-ecosys.com>
From: Andreas Kretschmer <andreas@a-kretschmer.de>
In-Reply-To: <e4688faf-de51-93ef-2db-f2acacbd658@appl-ecosys.com>
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Am 10.09.24 um 17:07 schrieb Rich Shepard:
> I've no idea how I entered multiple, identical rows in a table but I 
> want to
> delete all but one of these rows.
>
> Here's an example:
>
> bustrac=# select * from projects where proj_nbr = '4242.01';
>  proj_nbr |   proj_name    | start_date |  end_date  | description  | 
> notes 
> ----------+----------------+------------+------------+---------------+-------
>  4242.01  | Expert witness | 2008-10-15 | 2008-10-28 | Consol Energy |
>  4242.01  | Expert witness | 2008-10-15 | 2008-10-28 | Consol Energy |
>  4242.01  | Expert witness | 2008-10-15 | 2008-10-28 | Consol Energy |
>  4242.01  | Expert witness | 2008-10-15 | 2008-10-28 | Consol Energy | 
> (4 rows)
>
> How do I clean this up so there's only a single row for this project 
> number?
>
> TIA,
>
> Rich
>
>

you can use the hidden ctid-column:

postgres=# create table demo (id int, val text);
CREATE TABLE
postgres=# insert into demo values (1, 'test1');
INSERT 0 1
postgres=# insert into demo values (1, 'test1');
INSERT 0 1
postgres=# insert into demo values (1, 'test1');
INSERT 0 1
postgres=# insert into demo values (1, 'test1');
INSERT 0 1
postgres=# select ctid, * from demo;
  ctid  | id |  val
-------+----+-------
  (0,1) |  1 | test1
  (0,2) |  1 | test1
  (0,3) |  1 | test1
  (0,4) |  1 | test1
(4 rows)

postgres=# with my_ctid as (select min(ctid) from demo where id = 1 and 
val = 'test1') delete from demo using my_ctid where id=1 and val='test1' 
and ctid != my_ctid.min;
DELETE 3
postgres=# select ctid, * from demo;
  ctid  | id |  val
-------+----+-------
  (0,1) |  1 | test1
(1 row)

postgres=#


-- 
Andreas Kretschmer
CYBERTEC PostgreSQL Services and Support