How To Add Sequence Column To Existing Table With Records

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'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"