php脚本不返回第一个数组

this PHP script is supposed to return the top five losers, the top five gainers and the five most active stocks in the form of arrays called result. when i run the query in the database it returns the right values but when i run the PHP script in the browser it doesn't return the first array, it starts from the second array ,the second array and so on. this is the script:

    switch ($which){
        case 'top':
            $sql = "SELECT * FROM market_table ORDER BY price_change DESC LIMIT 5";
            $result = $this -> connection->query($sql);
            if($result->num_rows > 0){
                $r = mysqli_query($this->connection,$sql);
                $res = mysqli_fetch_array($r);
                $result = array(); 
                while($res = mysqli_fetch_array($r)){
                    array_push($result,array("sympol"=>$res['sympol'],"o_price"=>$res['o_price'],
                    'e_name'=>$res['e_name'], 'price_change'=>$res['price_change'],'perc_change'=>$res['perc_change'],
                    'c_price'=>$res['c_price'],'volume'=>$res['volume'],'h_price'=>$res['h_price'],
                    'l_price'=>$res['l_price'],'deals_n'=>$res['deals_n'],
                    'value'=>$res['value']));
                }
                echo json_encode(array("result"=>$result));
            }           
            else{
                echo "top five: 0 results";
            }
        break;
        case 'bottom':
            $sql = "SELECT * FROM market_table ORDER BY price_change ASC LIMIT 5";
            $result = $this -> connection->query($sql);
            if($result->num_rows > 0){
                $r = mysqli_query($this->connection,$sql);
                $res = mysqli_fetch_array($r);
                $result = array(); 
                while($res = mysqli_fetch_array($r)){
                    array_push($result,array("sympol"=>$res['sympol'],"o_price"=>$res['o_price'],
                    'e_name'=>$res['e_name'], 'price_change'=>$res['price_change'],'perc_change'=>$res['perc_change'],
                    'c_price'=>$res['c_price'],'volume'=>$res['volume'],'h_price'=>$res['h_price'],'l_price'=>$res['l_price'],
                    'deals_n'=>$res['deals_n'],
                    'value'=>$res['value']));
                }
                echo json_encode(array("result"=>$result));
            }           
            else{
                echo "bottom five: 0 results";
            }
        break;
        case'most':
            $sql = "SELECT * FROM market_table ORDER BY deals_n DESC LIMIT 5";
            $result = $this -> connection->query($sql);
            if($result->num_rows > 0){
                $r = mysqli_query($this->connection,$sql);
                $res = mysqli_fetch_array($r);

                $result = array(); 
                while($res = mysqli_fetch_array($r)){
                    array_push($result,array("sympol"=>$res['sympol'],"o_price"=>$res['o_price'],
                    'e_name'=>$res['e_name'], 'price_change'=>$res['price_change'],'perc_change'=>$res['perc_change'],
                    'c_price'=>$res['c_price'],'volume'=>$res['volume'],'h_price'=>$res['h_price'],'l_price'=>$res['l_price'],
                    'deals_n'=>$res['deals_n'],
                    'value'=>$res['value']));
                }
                echo json_encode(array("result"=>$result));
            }           
            else{
                echo "most active five: 0 results";
            }
        break;
    }

$res = mysqli_fetch_array($r);
$result = array();

Why do you have those? You're not saving the result($res) since you're initializing the result($result) to an empty array on the 2nd line. So that's where your first line disappears.