在codeigniter中订购group_by

Question

i have a table

id  typesignal close open cont

1    4    150    300    2

2    3    20    40    1

3    2    50    75    15

4    1    15.2    30.8    5

5    1    200    225    8

6    6    200    500    8

7    7    10    20    4

8    8    9    12    2

9    9    5    8    3

10    5    40    50    4

11    4    5    8    9

12    5    4    2    3

13    8    5    4    0

i want to display the last row of each kind from the typesignal column.

$this->db->group_by('typesignal');
$query = $this->db->get('signals');

but I need the last row that was create i use

$this->db->group_by('typesignal');
$this->db->order_by("idSignal");
$query = $this->db->get('signals');

but its not working.

The expected output is: 13,12,11,9,8,7,6,5,3,2

Answer 1

i use this query

$this->db->group_by('typeSignal');


$this->db->select_max('idSignal');


$this->db->order_by("idSignal", "DESC");            


$query = $this->db->get('signals');


return $query->result_array();

is working the secret is $this->db->select_max('idSignal');

Thanx for the help