PHP进行数据库信息修改，数据库连接正常，但是一直修改不成功，求大神指教？
<?php
session_start();
include "../config.php";
if(!isset($_SESSION['username'])){
echo "<script type=\"text/javascript\"> window.location.href=\"login.php\" </script>";
}
if($_GET['yid']){
$yid=$_GET['yid'];
$su="select * from yh where yid='$yid'";
$reu=$conn->query($su);
$reut=$reu->fetch_assoc();
}
if(isset($_GET['edit'])){
$xm=$_POST['xm'];
$password=$_POST['password'];
$xb=$_POST['xb'];
$zzbm=$_POST['zzbm'];
$dhhm=$_POST['dhhm'];
$js=$_POST['js'];
$twsp=0;
$ldsp=0;
if($js==1){
$twsp=1;
}
elseif(($js==2)){
$ldsp=1;
}
$sql="update yh set xm='$xm',password='$password',xb='$xb',zzbm='$zzbm',ddhm='$dhhm',twsp='$twsp',ldsp='$ldsp' where yid='$yid'";
$UPDATE=$conn->query($sql);
}
?>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>学生信息添加</title>
<link rel="stylesheet" type="text/css" href="../layui-v2.6.7/layui/css/layui.css"/>
<script src="../layui-v2.6.7/layui/layui.js" type="text/javascript" charset="utf-8"></script>
</head>
<body>
<form class="layui-form" action="yhxg.php?edit=1&yid=<?php echo $reut['yid'];?>" method="post">
<div class="layui-form-item">
<label class="layui-form-label">姓名</label>
<div class="layui-input-block">
<input type="text" name="xm" value="<?php echo $reut['xm'];?>" required lay-verify="required" placeholder="请填写真实姓名" autocomplete="off" class="layui-input">
</div>
</div>
<div class="layui-form-item">
<label class="layui-form-label">登录密码</label>
<div class="layui-input-inline">
<input type="password" name="password" value="<?php echo $reut['password'];?>" required lay-verify="required" placeholder="请输入密码" autocomplete="off" class="layui-input">
</div>
<div class="layui-form-mid layui-word-aux">为保证安全，建议密码为数字加字母</div>
</div>
<div class="layui-form-item">
<label class="layui-form-label">性别</label>
<div class="layui-input-block">
<input type="radio" name="xb" <?php if($reut['xb']=='男'){ echo "checked=\"checked\"";} ?> value="男" title="男" required="required">
<input type="radio" name="xb" <?php if($reut['xb']=='女'){ echo "checked=\"checked\"";} ?> value="女" title="女" required="required">
</div>
</div>
<div class="layui-form-item">
<label class="layui-form-label">组织部门</label>
<div class="layui-input-block">
<input type="text" name="zzbm" value="<?php echo $reut['zzbm'];?>" required lay-verify="required" placeholder="请输入组织部门" autocomplete="off" class="layui-input">
</div>
</div>
<div class="layui-form-item">
<label class="layui-form-label">手机号码</label>
<div class="layui-input-block">
<input type="text" name="dhhm" value="<?php echo $reut['dhhm'];?>" required lay-verify="required" placeholder="请填写手机号码" autocomplete="off" class="layui-input">
</div>
</div>
<div class="layui-form-item">
<label class="layui-form-label">用户角色</label>
<div class="layui-input-block">
<input type="radio" name="js" <?php if($reut['twsp']=='0'&&$reut['ldsp']=='0'){ echo "checked=\"checked\"";} ?> value="0" title="普通用户" >
<input type="radio" name="js" <?php if($reut['twsp']=='1'){ echo "checked=\"checked\"";} ?> value="1" title="团委审批人" >
<input type="radio" name="js" <?php if($reut['ldsp']=='1'){ echo "checked=\"checked\"";} ?> value="2" title="领导审批人" >
</div>
</div>
<div class="layui-form-item">
<div class="layui-input-block">
<button class="layui-btn" lay-submit lay-filter="formDemo">立即提交</button>
<button type="reset" class="layui-btn layui-btn-primary">重置</button>
<a href="yh.php"><button type="button" class="layui-btn layui-btn-primary">返回</button></a>
</div>
</div>
</form>
<script >
//使用layui的多个模块
layui.use(['form','laydate','layer'],function(){
var form = layui.form;
var layer = layui.layer;
//各种监听事件
<?php if($insert){?>
layer.msg('修改成功！');
<?php }?>
});
</script>
</body>
</html>
$sql="update yh set xm='{$xm}',password='{$password}',xb='{$xb}',zzbm='{$zzbm}',ddhm='{$dhhm}',twsp='{$twsp}',ldsp='{$ldsp}' where yid='{$yid}'";
$UPDATE=$conn->exec($sql);