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help / color / mirror / Atom feedFrom: Peter Eisentraut <[email protected]>
To: Colin 't Hart <[email protected]>
To: [email protected]
Subject: Re: Two sequences associated with one identity column
Date: Wed, 29 Oct 2025 17:01:12 +0100
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAMon-aTbZC5k2pLpijk5x+h__LV08DzpoJtHBgZGkOKJNJ91pw@mail.gmail.com>
References: <CAMon-aTbZC5k2pLpijk5x+h__LV08DzpoJtHBgZGkOKJNJ91pw@mail.gmail.com>
On 29.10.25 12:27, Colin 't Hart wrote:
> One of my clients has a database in which a single identity column
> (called "id" in that table) has two sequences associated with it(!)
>
> Both sequences display
>
> Sequence for identity column: <schema>.<table>.id
>
> when described with \d in psql.
>
>
> Inserting fails with "ERROR: more than one owned sequence found", as
> does trying to alter the table to drop the identity on that column.
>
>
> Trying to drop either sequence results in
>
> ERROR: cannot drop sequence <name> because column id of table <name>
> requires it
> HINT: You can drop column id of table <name> instead.
>
> while trying to alter either sequence "owned by none" results in
>
> ERROR: cannot change ownership of identity sequence
> DETAIL: Sequence "<name>" is linked to table "<name>".
>
>
> How do we fix this? I presume we need to update the catalog directly
> to dissociate one of the sequences and after that drop the orphaned
> sequence.
I don't know how one would get into this situation, but I can fake it
like this:
create table t1 (a int, b int generated always as identity);
select * from pg_depend where refclassid = 'pg_class'::regclass and
refobjid = 't1'::regclass;
classid | objid | objsubid | refclassid | refobjid | refobjsubid | deptype
---------+-------+----------+------------+----------+-------------+---------
1247 | 16388 | 0 | 1259 | 16386 | 0 | i
1259 | 16384 | 0 | 1259 | 16386 | 2 | i
(2 rows)
The second entry is the dependency between the sequence and the table.
1259 is pg_class, the numbers 16384 and 16386 are the OIDs of the
sequence and the table, and 2 is the column number.
Now create another sequence and manually insert a dependency record:
create sequence sx;
insert into pg_depend values (1259, 'sx'::regclass, 0, 1259, 16386, 2, 'i');
Now you have the same breakage:
insert into t1 (a) values (1);
ERROR: more than one owned sequence found
To fix this, remove the extra dependency record:
delete from pg_depend where (classid, objid, objsubid) =
('pg_class'::regclass, 'sx'::regclass, 0) and (refclassid, refobjid,
refobjsubid) = ('pg_class'::regclass, 't1'::regclass, 2) and deptype = 'i';
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