PHPStorm中$db报错

问题遇到的现象PHPStorm中使用$db无法全局使用

问题相关代码

我已经使用global $db 在后面函数中还是无法使用
getMessage(); } ?>

报错内容 在第十二行

<?php
include"conn.php";//包含连接数据库的PHP文件
include"stuInfo.php";//包含前端页面的PHP页
//以post方式接收stuinfo.PHP页面提交的表单数据
$sno=@$_POST['sno'];
$sname=@$_POST['sname'];
$ssex=@$_POST['ssex'];
$sbirthday=@$_POST['sbirthday'];
$speciality=@$_POST['speciality'];
$tc=@$_POST['tc'];

$search_sql="select * from student where sno='$sno'";
$search_result=$db->query($search_sql);

//录入功能
if(@$_POST['btn']=='录入'){
    $count=$search_result->rowCount();
    if($search_result->rowCount()!=0)//要录入的学号已经存在时提示
        echo"<script>alert('该学生已经存在！');location.href='stuInfo.php';</script>";
    else{
        $ins_sql="insert into student values('$sno','$sname','$ssex','$sbirthday','$speciality','$tc')";
        $ins_result=$db->query($ins_sql);
        if($ins_result->rowCount()!=0){
            echo"<script>alert('录入成功！'); location.href='stuInfo.php';</script>";
        }else
        echo"<script>alert('录入失败，请检查输入信息！'); location.href='stuInfo.php';</script>";
    }
}

//删除功能
if(@$_POST['btn']=='删除'){
    $_SESSION['sno']=$sno;
    if($search_result->rowCount()==0)//要删除的学号不存在时提示
        echo"<script>alert('该学生不存在！');location.href='stuInfo.php';</script>";
    else{
        $del_sql="delete from student where sno='$sno'";
        $del_affected=$db->exec($del_sql);
        if($del_affected){
            $_SESSION['sno']='';
            $_SESSION['sname']='';
            $_SESSION['ssex']='';
            $_SESSION['sbirthday']='';
            $_SESSION['speciality']='';
            $_SESSION['tc']='';
            echo"<script>alert('删除成功！'); location.href='stuInfo.php';</script>";
        }
    }
}

//更新功能
if(@$_POST['btn']=='更新'){
    $_SESSION['sno']=$sno;
    $upd_sql="update student set sno='$sno',sname='$sname',ssex='$ssex',sbrithay='$sbirthday',speciality='$speciality',tc='$tc' where sno='$sno'";
    $upd_affected=$db->exec($upd_sql);
    if(upd_affected){
        $_SESSION['sno']='';
            $_SESSION['sname']='';
            $_SESSION['ssex']='';
            $_SESSION['sbirthday']='';
            $_SESSION['speciality']='';
            $_SESSION['tc']='';
            echo"<script>alert('更新成功！');location.href='stuInfo.php';</script>";
    }
    else
            echo"<script>alert('更新失败，请检查输入信息！'); location.href='stuInfo.php';</script>";
}

//查询功能
if(@$_POST['btn']=='查询'){
    $_SESSION['sno']=$sno;
    $find_sql="select * from student where sno='$sno'";
    $find_result=$db->query($find_sql);
    if($find_result->rowCount()==0)
            echo"<script>alert('该学生不存在！');location.href='stuInfo.php';</script>";
    else{
        list($sno,$sname,$ssex,$sbirthday,$speciality,$tc)=$find_result->fetch(PDO::FETCH_NUM);
        $_SESSION['sno']=$sno;
            $_SESSION['sname']=$sname;
            $_SESSION['ssex']=$ssex;
            $_SESSION['sbirthday']=$sbirthday;
            $_SESSION['speciality']=$speciality;
            $_SESSION['tc']=$tc;
            echo"<script>location.href='stuInfo.php';</script>";
    }  
} 
?>

###### 我想要达到的结果
解决这个报错让他正常使用