How to add a sequence column to an existing table with records - sql

Question

I had created a new table named USERLOG with two fields from a previous VIEW. The table already consist of about 9000 records. The two fields taken from the VIEW, i.e. weblog_views consist of IP (consists of IP address), and WEB_LINK (consists of URL). This is the code I used,
CREATE TABLE USERLOG
AS
SELECT C_IP, WEB_LINK FROM weblog_views;
I want to add another column to this table called the USER_ID, which would consists of a sequence starting with 1 to 9000 records to create a unique id for each existing rows. I need help with this part. I'm using Oracle SQL Developer: ODMiner version 3.0.04.
I tried using the AUTO-INCREMENT option,
ALTER TABLE USERLOG
ADD USER_ID INT UNSIGNED NOT NULL AUTO_INCREMENT;
But I get an error with this,
Error report:
SQL Error: ORA-01735: invalid ALTER TABLE option
01735. 00000 - "invalid ALTER TABLE option"
So, I would really appreciate any help that I can get!

Answer 1

You would need to add a column
ALTER TABLE userlog
ADD( user_id number );
create a sequence
CREATE SEQUENCE user_id_seq
START WITH 1
INCREMENT BY 1
CACHE 20;
Update the data in the table
UPDATE userlog
SET user_id = user_id_seq.nextval
Assuming that you want user_id to be the primary key, you would then add the primary key constraint
ALTER TABLE userlog
ADD CONSTRAINT pk_user_id PRIMARY KEY( user_id );
If you want to use the sequence to automatically add the user_id when you do an INSERT (the other option would be to specifically reference user_id_seq.nextval in your INSERT statements, you would also need a trigger
CREATE OR REPLACE TRIGGER trg_userlog_user_id
BEFORE INSERT ON userlog
FOR EACH ROW
BEGIN
:new.user_id := user_id_seq.nextval;
END;

Answer 2

In addition to Justin's excellent answer you might want to prevent NULL values for your user_id in the future (as they could still be caused by UPDATE statements). Therefore, execute the following statement at the end:
ALTER TABLE userlog MODIFY(user_id number NOT NULL);

Answer 3

Step 1.
Create sequence to be used by the column
eg:
CREATE SEQUENCE user_id_seq
START WITH 1
INCREMENT BY 1
CACHE 20;
Step 2.
Update new column with sequence
eg:
UPDATE userlog
SET user_id = user_id_seq.nextval;
Step 3. - Set Sequence as the default value for the column, will work only above Oracle 12c
ALTER TABLE USERLOG
MODIFY USER_ID INT DEFAULT user_id_seq.nextval;