无法删除CodeIgniter中数据库中最旧的记录

Question

I made a website using CodeIgniter framework. I have a user system and I am trying to keep in my database only the last 5 logins. Here is the code I have written:

$logins = array(
   'uid'  => $user['id'],
   'time' => now(),
   'ip'   => $this->input->ip_address()
);
$this->db->insert('logins', $logins);
$this->db->where('uid', $user['id']);
$logins_no = $this->db->count_all_results('logins');
$logins_deleted = $logins_no - 5;
if ($logins_deleted > 0) {
    $this->db->where('uid', $user['id']);
    $this->db->order_by('time asc');
    $this->db->limit($logins_deleted);
    $this->db->delete('logins');
}

So basically, I am inserting the date and IP when a user is connecting then I count all the records of the user in the logins table from the database. If there are more than 5 logins I count how many results I have to delete.

Why it isn't working?

Answer 1

SQL doesn't allow for an ORDER BY clause to be part of a DELETE query so you'll have to do as Jeemusu suggested:

Get an unique identifier of the rows you intend to delete. You haven't specified whether or not you have a primary column (you should) so we'll just go with the time column for the sake of the explanation:

$query = $this->db->where('uid', $user['id'])->order_by('time asc')->limit(5)->get('logins');
$result = $query->result();

Create an array with the values of the time columns:

$times = array();
foreach($result as $r) {
    $times[] = $r->time;
}

Now use the where_in method of Active Record to delete these rows:

$this->db->where_in('time', $times)->where('uid', $user['id'])->delete('logins');

You can disregard the second where method used if you go for deleting based on the primary key.