Re: Adding identity column to a non-empty table

On Sun, Oct 15, 2017 at 8:24 PM, Igal @ Lucee.org <igal(at)lucee(dot)org> wrote:

> On 10/15/2017 4:01 PM, Igal @ Lucee.org wrote:
>
>>
>> Hello,
>>
>> I'm trying to add an identity column to a table that has records
>> (previously had a bigserial column which I removed):
>>
>> ALTER TABLE event_log
>> ADD COLUMN r_id BIGINT GENERATED BY DEFAULT AS IDENTITY;
>>
>> But I'm getting an error `column r_id contains null values`.
>>
>> How can I add the column and populate it for the existing rows?
>>
>>
> There is probably a better solution, but the one I came up with is to add
> the column as BIGSERIAL and DROP the SEQUENCE CASCADE, SELECT the max(rid)
> + 1, and then convert the column to IDENTITY:
>
> ALTER TABLE transient.event_log ADD COLUMN r_id BIGSERIAL;
>
> -- find the sequence name and then
> DROP sequence <sequence-name> CASCADE;
>
> -- find min value by executing select max(r_id) + 1
> ALTER table transient.event_log
> ALTER COLUMN r_id
> ADD GENERATED BY DEFAULT AS IDENTITY (MINVALUE <min-value>);
>
> If anyone has a better suggestion then please let me know.
>
> Thanks,
>
>
> Igal
>
>
>
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The correct way to make r_id the primary key would be:

ALTER TABLE event_log
ADD COLUMN r_id SERIAL;

ALTER TABLE event_log
ALTER COLUMN r_id TYPE BIGINT,
ADD CONSTRAINT dummy_pk PRIMARY KEY (r_id);

That automatically generates the column as

r_id bigint NOT NULL DEFAULT nextval('dummy_r_id_seq'::regclass),
CONSTRAINT dummy_pk PRIMARY KEY (r_id)

and creates the appropriate sequence for you.

--
*Melvin Davidson*
I reserve the right to fantasize. Whether or not you
wish to share my fantasy is entirely up to you.