CodeIgniter - Group by with order by not working a

问题:

So I got this query:

    $CI->db->where('user_id', $CI->session->userdata('user_id'));
    $CI->db->where('amount >', 0);
    $CI->db->order_by('ur_time', 'desc');
    $CI->db->group_by('resource_id');
    $query = $CI->db->get('users_resources');
    $resources = $query->result();

My problem is: The order_by 'ur_time' doesn't really work. If I got 2 rows, one with amount 10000 and ur_time 1384303464 and another row with amount 100 and ur_time 1384304656 I still get the row with amount 10000 as result.

What am I doing wrong?

EDIT: Maybe I have to explain it a bit. Let's say I got some rows:

ur_id | ur_time     | user_id | resource_id | amount

1     | 1384304656  | 1       | 1           | 100
2     | 1384303464  | 1       | 1           | 10000
3     | 1384303464  | 1       | 2           | 200
4     | 1384304656  | 1       | 2           | 20000

What I'd like to get here as result: Two rows, the one with ur_id 1 and the one with ur_id 4 because for each resource_id I want the row with the highest ur_time. I hope it's clear now.

PS: I need the amount > 0 clause because there can be negative amounts but I don't want them in the result.

回答1:

Try adding this in your query see if they will combine in your select statement

$CI->db->select('*');
$CI->db->select_max('ur_time' , 'max_ur_time'); // this will produce max(ur_time) as max_ur_time
$CI->db->where('user_id', $CI->session->userdata('user_id'));
$CI->db->where('amount >', 0);
$CI->db->order_by('ur_time', 'desc');
$CI->db->group_by('resource_id');
$query = $CI->db->get('users_resources');
$resources = $query->result();