RE: Sequence Cycle question

Lets say I was to set the cycle=true. Once the IDs start back at 1, lets say we get to an ID of 5 where there is a duplicate.

Is there a trigger or something else, that I could associate with the table that would "catch/detect" the insert error. If an error occurs it would then do a "fresh" insert with no specified ID so the sequence would naturally be incremented?

I hope that made sense.

Thanks,

-----Original Message-----
From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Sent: Thursday, January 23, 2025 11:42 AM
To: Campbell, Lance <lance(at)illinois(dot)edu>
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: Sequence Cycle question

"Campbell, Lance" <lance(at)illinois(dot)edu> writes:
> Table X has records that have been removed over time randomly. There are IDs that cover a wide range of values between 1 and 1,000,000.
> When the primary key ID, which is a sequence, reaches 1,000,000 then the next sequence value will start back at 1.
> What would happen if I had a primary key for ID of 5 still in use? When I reach 5 will the sequence skip that number and go to 6 instead?

No, the sequence has no idea about what is in the table. It will generate "5" when it's time to, and then your insert will get a duplicate-key violation.

You could work around that by retrying the insert, but it might be better to reconsider whether you want a cycling sequence for this application.

regards, tom lane