PHP实现简单用户登录界面

<form action="connet.php" method="POST"  
用户名：<input type = "text" name = "username"/  <br / 
密码：<input type = "password" name="password"/  <br / 
重复密码：<input type = "password" name="repassword"/ <br / 
<input type = "submit" value = "提交"/ 
</form 

<?php
if(trim($_POST['password'])!=trim($_POST['repassword'])){
 exit('两次密码不一致，请返回上一页');
} 
 //$_POST用户名和密码
 $username = $_POST['username'];
 $password = $_POST['password'];
 //连接mysql
 $con = mysqli_connect('localhost','root','');
 //验证mysql连接是否成功
if(mysqli_errno($con)){
 echo "连接mysql失败：".mysqli_error($con);
 exit;
}
//设置数据库字符集
 mysqli_set_charset($con,'utf8');
 //查看数据库emp
 mysqli_select_db($con,'emp');
 //查看表sgbf用户名与密码和传输值是否相等
 $sql = "select *from sgbf where username='$username' and password='$password'";
 //result必需规定由 mysqli_query()、mysqli_store_result() 或 mysqli_use_result() 返回的结果集标识符。
 $result = mysqli_query($conn,$sql);
 $num = mysqli_num_rows($result);// 函数返回结果集中行的数量
 if($num){
 
 echo '成功';
 }else{
 echo'失败';
 }
 mysqli_close($con);
 ?