Active record in codeigniter

Just try this one and let me know,

$this->db->select("b.name,SUM(CASE WHEN c.size = 'S' THEN 1 ELSE 0 END) S,SUM(CASE WHEN c.size = 'M' THEN 1 ELSE 0 END) M,SUM(CASE WHEN c.size = 'L' THEN 1 ELSE 0 END) L,SUM(CASE WHEN c.size = 'XL' THEN 1 ELSE 0 END) XL", FALSE );$this->db->from('orderTB a');$this->db->join('productTB b','a.id_product = b.id_shirt','inner');$this->db->join('sizeTB c','a.id_size = c.id_size','inner');$this->db->group_by('b.name');

From document here

$this->db->select() accepts an optional second parameter. If you set it to FALSE, CodeIgniter will not try to protect your field or table names with backticks. This is useful if you need a compound select statement.

EDIT

Just add FALSE in your select statement

function get() {    $this->db->select("b.name,SUM(CASE WHEN c.size ='S' THEN 1 ELSE 0 END) as S,SUM(CASE    WHEN c.size = 'M' THEN 1 ELSE 0 END) as M,SUM(CASE WHEN c.size = 'L' THEN 1 ELSE 0 END) as   L,SUM(CASE WHEN c.size = 'XL' THEN 1 ELSE 0 END) as XL",FALSE);    $this->db->from('order');    $this->db->join('ukuran','order.id_size=ukuran.id_size');    $this->db->where('date',$date);    return $this->db->get();}