how to auto increment variable - php

Question

I need some quick help, I need to know if I can somehow increment the $user_id by one so that I do not get a duplicate entry error. Do I just add a +1 after ['user_id']?
public function insert_video($video_id,$user_id,$caption) {
$userObject = array();
$userObject['user_id'] = $user_id;
$userObject['video_id'] = $video_id;
$userObject['caption'] = str_replace(array("'",'"'), '', $caption);
$userObject['description'] = '';
$userObject['votes'] = 0;
$userObject['upload_time'] = date('Y-m-d H:i:s');
$userObject['version'] = $this->contests->contest->version; //4
//if($this->contests->contest->auto_approve)
$userObject['approved'] = 1;
$this->db->insert('photos', $userObject);
return $this->db->insert_id();
ok guys I edited the function and removed any mention of user_id but for some reason I still get the error when I try to submit another video. Should I try dropping that column on the table? here is my updated function
public function insert_video($video_id,$caption) {
$userObject = array();
//$userObject['user_id'] = $user_id+1;
$userObject['video_id'] = $video_id;
$userObject['caption'] = str_replace(array("'",'"'), '', $caption);
$userObject['description'] = '';
$userObject['votes'] = 0;
$userObject['upload_time'] = date('Y-m-d H:i:s');
$userObject['version'] = $this->contests->contest->version; //4
//if($this->contests->contest->auto_approve)
$userObject['approved'] = 1;
$this->db->insert('photos', $userObject);
return $this->db->insert_id();
}

Answer 1

You need to set up your user_id To auto increment. If you find it easier as you clearly have a table already set up, use phpMyAdmin to set the AI tick box to true.
Then when you INSERT, you'll get a unique value. You do not need to specify the user_id as that'll be taken care of.
INSERT INTO users (FirstName,LastName) VALUES ('Matt','HB')

Answer 2

I suppose you need to have 2 tables, one that holds a user info with auto incresment column e.g. "ID".
In table photos don't use auto incresment for user_id, as you need to give users ability to insert multiple photos and update current. just change in your table:
`user_id` to `ID` -> this will auto incresment
create new column `user_id` int 200.. this will be a reference of `column - "ID"` from **userinfo** table;
//then run your query:
INSERT INTO photos (user_id, video_id, caption, description, votes, upload_time, version, approved) VALUES (7339, 'fDTm1IzQf-U', 'new test', '', 0, '2014-11-12 16:17:36', '19', 1)