php表单插入数据库，求大神帮忙

<code><?php      if(!isset($_POST['submit'])){          //如果没有表单提交，显示一个表单  ?>      <form action="" method="post">     <table>        <tr>          <td>请输入姓名：<input type="text" name="username"></td>        </tr>        <tr>          <td>请输入电话：    <input type="text" name="mobile"></td>        </tr>        <tr>          <td>请确认城市：    <input type="text" name="city"></td>        </tr>        <tr>          <td>请输入邮箱：<input type="text" name="emile"></td>        </tr>        <tr>          <td><input type="submit" value="报名">    <input type="reset" value="重置"></td>        </tr>      </table>    </form>  <?php      }      else      {          //如果提交了表单          //数据库连接参数          $host = "localhost";          $user = "root";          $pass = "";          $db = "anxinjia";          //取得表单中的值，检查表单中的值是否符合标准，并做适当转义，防止SQL注入         $username=$_POST['username'];  $mobile=$_POST['mobile'];  $city=$_POST['city'];   $emile=$_POST['emile'];          //打开数据库连接          $connection = mysql_connect($host, $user, $pass) or die("Unable to connect!");          //选择数据库          mysql_select_db($db) or die("Unable to select database!");          //构造一个SQL查询          $query = "INSERT INTO shuipf_AttractInvestment(username, mobile, city,emile) VALUES('$username', '$mobile', '$city','$emile')";          //执行该查询          $result = mysql_query($query) or die("Error in query: $query. ".mysql_error());          //插入操作成功后，显示插入记录的记录号          echo "记录已经插入， mysql_insert_id() = ".mysql_insert_id();          //关闭当前数据库连接          mysql_close($connection);      }  ?></code>