MySQL データベース データを JSON 配列に変換するにはどうすればよいですか?

$return_arr = array();

$fetch = mysql_query("SELECT * FROM table"); 

while ($row = mysql_fetch_array($fetch, MYSQL_ASSOC)) {
    $row_array['id'] = $row['id'];
    $row_array['col1'] = $row['col1'];
    $row_array['col2'] = $row['col2'];

    array_push($return_arr,$row_array);
}

echo json_encode($return_arr);

[{"id":"1","col1":"col1_value","col2":"col2_value"},{"id":"2","col1":"col1_value","col2":"col2_value"}]

$year = date('Y');
$month = date('m');

$json_array = array();

//Fetch data from database and populate the JSON array
foreach ($data from database as $row) {
    $json_array[] = array(
        'id' => $row['id'],
        'title' => $row['title'],
        'start' => $year . '-' . $month . '-' . $row['start_date'],
        'end' => $year . '-' . $month . '-' . $row['end_date'],
        'url' => $row['url']
    );
}

echo json_encode($json_array);