memfilter data yang bernilai '<0', '>0', dan '=0' pada php mysql framework codeigniter

Kodingan dibawah untuk sistem inventory. Total Stok barang ini hasil dari penambahan total dari setiap gudang (total ada 11 gudang), pada Total Stok barangnya ada yang bernilai plus dan minus. Saya mau memfilter pada bagian view agar bisa memilih barang mana yang memiliki nilai Total Stok yang plus (> 0), Minus (< 0), atau Nol (= 0)

Kodingan Controllernya

$product_name           = $this->input->get('product_name') ? $this->input->get('product_name') : null;
$product                = $this->input->get('product') ? $this->input->get('product') : null;
$stock                  = $this->input->get('stock') ? $this->input->get('stock') : null;

$this->load->library('datatables');

            // Subquery buat jumlah tiap wh
            $this->db->select('product_id, 
                MAX(CASE WHEN warehouse_id = 1 THEN quantity ELSE NULL END) AS whqty1,
                MAX(CASE WHEN warehouse_id = 2 THEN quantity ELSE NULL END) AS whqty2,
                MAX(CASE WHEN warehouse_id = 3 THEN quantity ELSE NULL END) AS whqty3,
                MAX(CASE WHEN warehouse_id = 4 THEN quantity ELSE NULL END) AS whqty4,
                MAX(CASE WHEN warehouse_id = 5 THEN quantity ELSE NULL END) AS whqty5,
                MAX(CASE WHEN warehouse_id = 6 THEN quantity ELSE NULL END) AS whqty6,
                MAX(CASE WHEN warehouse_id = 7 THEN quantity ELSE NULL END) AS whqty7,
                MAX(CASE WHEN warehouse_id = 8 THEN quantity ELSE NULL END) AS whqty8,
                MAX(CASE WHEN warehouse_id = 9 THEN quantity ELSE NULL END) AS whqty9,
                MAX(CASE WHEN warehouse_id = 10 THEN quantity ELSE NULL END) AS whqty10,
                MAX(CASE WHEN warehouse_id = 11 THEN quantity ELSE NULL END) AS whqty11',
                false)
                ->from('warehouses_products')
                ->group_by('product_id');
            $warehouse_quantities_subquery = $this->db->get_compiled_select();

            // Main query
            $this->datatables
                ->select("
                    {$this->db->dbprefix('products')}.id as productid, 
                    {$this->db->dbprefix('products')}.image as image, 
                    {$this->db->dbprefix('products')}.barcode_product as code, 
                    {$this->db->dbprefix('products')}.name as name,
                    {$this->db->dbprefix('products')}.second_name as packing,
                    {$this->db->dbprefix('products')}.product_status as product_status,                    
                    wq.whqty1, 
                    wq.whqty2,        
                    wq.whqty3,
                    wq.whqty4, 
                    wq.whqty5,
                    wq.whqty6,
                    wq.whqty7,
                    wq.whqty8,
                    wq.whqty9,
                    wq.whqty10,
                    wq.whqty11,
                    (COALESCE(wq.whqty1, 0) + COALESCE(wq.whqty2, 0) + COALESCE(wq.whqty3, 0) + COALESCE(wq.whqty4, 0) + COALESCE(wq.whqty5, 0) + COALESCE(wq.whqty6, 0) + COALESCE(wq.whqty7, 0) + COALESCE(wq.whqty8, 0) + COALESCE(wq.whqty9, 0) + COALESCE(wq.whqty10, 0) + COALESCE(wq.whqty11, 0))"     
            
        , false)
        ->from('products')
        ->join("($warehouse_quantities_subquery) wq", 'wq.product_id = products.id', 'left')
        ->join('users', 'products.created_by=users.id', 'left')
        ->join('companies', 'products.supplier1=companies.id', 'left')
        ->join('brands', 'products.brand=brands.id', 'left')            
        ->group_by('products.id');

        
        if ($product_name) {
            $this->datatables->like('products.name', $product_name, 'both');
        }
        if ($product) {
            $this->datatables->where('products.id', $product);
        }

        if ($stock == '>0') {
            $this->datatables->where('(COALESCE(wq.whqty1, 0) + COALESCE(wq.whqty2, 0) + COALESCE(wq.whqty3, 0) + COALESCE(wq.whqty4, 0) + COALESCE(wq.whqty5, 0) + COALESCE(wq.whqty6, 0) + COALESCE(wq.whqty7, 0) + COALESCE(wq.whqty8, 0) + COALESCE(wq.whqty9, 0) + COALESCE(wq.whqty10, 0) + COALESCE(wq.whqty11, 0)) > 0', null, false);
        } elseif ($stock == '<0') {
            $this->datatables->where('(COALESCE(wq.whqty1, 0) + COALESCE(wq.whqty2, 0) + COALESCE(wq.whqty3, 0) + COALESCE(wq.whqty4, 0) + COALESCE(wq.whqty5, 0) + COALESCE(wq.whqty6, 0) + COALESCE(wq.whqty7, 0) + COALESCE(wq.whqty8, 0) + COALESCE(wq.whqty9, 0) + COALESCE(wq.whqty10, 0) + COALESCE(wq.whqty11, 0)) < 0', null, false);
        } elseif ($stock == '=0') {
            $this->datatables->where('(COALESCE(wq.whqty1, 0) + COALESCE(wq.whqty2, 0) + COALESCE(wq.whqty3, 0) + COALESCE(wq.whqty4, 0) + COALESCE(wq.whqty5, 0) + COALESCE(wq.whqty6, 0) + COALESCE(wq.whqty7, 0) + COALESCE(wq.whqty8, 0) + COALESCE(wq.whqty9, 0) + COALESCE(wq.whqty10, 0) + COALESCE(wq.whqty11, 0)) = 0', null, false);
        }       
        
        } 
        echo $this->datatables->generate();

Dibawah ini Kodingan Viewnya

<?php
    $v = '';
    if ($this->input->post('product_name')) {
        $v .= '&product_name=' . $this->input->post('product_name');
    }
    if ($this->input->post('product')) {
        $v .= '&product=' . $this->input->post('product');
    }
    
    if($this->input->post('stock')){
        $v .= "&stock =" .$this->input->post('stock');
    }
    
?>

<div class="col-sm-6">
    <div class="form-group">
        <label class="control-label" for="stock"><?= lang('Stock Filter'); ?></label>
        <select name="stock" id="stock" class="form-control">
            <option value=""><?= lang('Select'); ?></option>
            <option value=">0" <?= (isset($_POST['stock']) && $_POST['stock'] == '>0') ? 'selected' : '' ?>><?= lang('Greater than 0'); ?></option>
            <option value="<0" <?= (isset($_POST['stock']) && $_POST['stock'] == '<0') ? 'selected' : '' ?>><?= lang('Less than 0'); ?></option>
            <option value="=0" <?= (isset($_POST['stock']) && $_POST['stock'] == '=0') ? 'selected' : '' ?>><?= lang('Equal to 0'); ?></option>
        </select>
    </div>
</div>

hasil dari kodingan diatas, tidak memfilter data sama sekali, saya sudah pakai fitur switch dan case juga sama saja. Tolong bantuannya dimana letak masalah dan perbaikannya. Terima kasih