How to get last row in each group in code igniter? [duplicate] - mysql

Question

I am working in codeigniter, i have a below table of schemes, my problem is i want to show last updated data of each scheme. I dont know how to do that, please help.
my_table
scheme_code updated_on scheme_name
1 2015-04-13 One
3 2015-04-12 Three
4 2015-04-13 Four
3 2015-04-10 Three
3 2015-04-8 Three
1 2015-04-10 One
4 2015-04-11 Four
My Model
function show_last_updated_data(){
$this->db->select('*');
$this->db->from('my_table');
$this->db->order_by('updated_on', 'DESC');
$query = $this->db->get();
return $query->result();
}
Output Needed
scheme_code updated_on scheme_name
1 2015-04-13 One
3 2015-04-12 Three
4 2015-04-13 Four

Answer 1

My answer is based on #Syed Qarib. I modified it to be compatible with codeigniter active record format.
function show_last_updated_data() {
$this->db->select('*, str_to_date(updated_on, "%Y-%M-%d") As date', false); // false to skip escape
$this->db->from('scheme');
$this->db->group_by('scheme_code');
$this->db->order_by('date', 'DESC');
$query = $this->db->get();
return $query->result();
}
Edit
In another way,
function show_last_updated_data() {
$max = $this->db->select_max("updated_on")->group_by("scheme_code")->get('scheme')->result_array();
$updated_on = array();
if (count($max)) {
$updated_on = array_column($max, "updated_on"); // make sure your php version is >= 5.5
}
$this->db->select("*");
$this->db->from("scheme");
$this->db->where_in("updated_on", $updated_on);
$query = $this->db->get();
return $query->result();
}
Hope it will be useful for you.

Answer 2

Try this:
function show_last_updated_data(){
$this->db->select('*');
$this->db->from('my_table');
$this->db->group_by('scheme_name');
$this->db->order_by('updated_on', 'DESC');
$query = $this->db->get();
return $query->result();
}

Answer 3

You need to use group by it will retrieve your record based on scheme_code without repeating it and your desire results. :)
function show_last_updated_data() {
$query = $this->db->select('*')
->from('my_table')
->group_by('scheme_code')
->order_by('updated_on', 'DESC')
->get();
return $query->result();
}

Answer 4

As you have used custom date format, so the ordering will not work correctly until you convert the string to date format. Try this:
function show_last_updated_data(){
$this->db->select('*, str_to_date(updated_on, "%Y-%M-%d") date');
$this->db->from('my_table');
$this->db->order_by('date', 'DESC');
$query = $this->db->get();
return $query->result();
}
Note: It is recommended to use native date/datetime field, do not use custom formats. You can also go for UNIX timestamp and save it in an int field. As the date can be fetched in any format afterwards and will save you hassle like this one.