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For serial columns used in Postgresql < 10, we manage the sequence by its name. We were able to reset a sequence with:

SELECT setval('table_id_seq', (SELECT MAX(id) FROM table));

From version 10, using identity columns, there is no need to use the sequence name. That's nice.

ALTER TABLE table ALTER COLUMN id RESTART WITH 1000;

How do I set the identity column to be the max(id) without knowing the sequence name?

As far as I can see from the ALTER TABLE syntax there is no way to have a subquery to compute the start of the sequence.

I would like to write something like:

ALTER TABLE table ALTER COLUMN id RESTART WITH (SELECT MAX(id) FROM table);
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1 Answer 1

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You can do the same with identity columns - they also use a sequence.

You can use pg_get_serial_sequence() to get the name of the sequence:

SELECT setval(pg_get_serial_sequence('the_table', 'id'), coalesce(MAX(id), 1))
from the_table;

The above works for serial and identity columns the same way.

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  • In case others have my same issue maybe there's an answer for them: This didn't work for me, because I always get that the sequence does not exist. When I SELECT * FROM information_schema.sequences , sure enough, there are no sequences anywhere to be found (even though I have a primary key as an identity column), so I try manually creating the sequence and assigning it to the table, and I get an error that it's an IDENTITY column (so I can't assign a manually created sequence I'm assuming?) So, I just gave up and went with a code based solution to do this instead of doing it directly in SQL. Commented Aug 30, 2023 at 5:47

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