PHP:运行后变量不工作“；如果“；命令

Recenty我计划创建一个数据库处理器，在处理登录信息后，包含数据的变量找不到（不显示），我试图在"if"中运行的任何程序都不会出现在屏幕上，该程序在我用javascript创建的弹出窗口后验证了登录信息。

登录信息是从登录屏幕发送的，这是发送数据的代码：登录

<form action="login1.php" method="post">
Username:<br><input type="text" name="uname">
<br>
Password:<br><input type="Password" name="pass">
<br>
<input type="submit" value="Login" name="submit">
</form>
</fieldset>
<form action="MainScreen.html" method='get'>
<button type='Submit'>Inapoi la pagina principala</button>
</form> 

这是处理登录信息的屏幕

<?php
require('sql_connect.php');
if (isset($_POST['submit'])){
    $username=mysql_escape_string($_POST['uname']);
    $password=mysql_escape_string($_POST['pass']);
    global $z;
    $z=substr($username, 0, -1);
    $q=$z;
    ///mysql_query($z);
    if (!$_POST['uname'] or !$_POST['pass']){
        echo ("<SCRIPT LANGUAGE='JavaScript'>
            window.alert('Nu ati completat toate campurile necesare.'nVa rugam incercati din nou.')
            window.location.href='login.php'
            </SCRIPT>");
    }
    $sql= mysql_query("SELECT * FROM `xii f` WHERE `IdPar` = '$username' AND `Password` = '$password'");
    if(mysql_num_rows($sql) > 0)
    {
        echo$z;
        echo ("<SCRIPT LANGUAGE='JavaScript'>
            window.alert('Bine ati venit domnule/doamna ".$z."')
            window.location.href='login1.php'
        </SCRIPT>");
        /* Here i tried to run a table, but it doesn't seem to work
        $sq= mysql_query("SELECT * FROM `absente s1` WHERE `Nume` ='$z'");
        echo'
            <table border="2" style= "background-color: white; color: black; margin: 3 auto; font-size:95%;" >
            <thead>
                <tr>
                    <th>Absenta</th>
                    <th>Materie</th>
                    <th>Motivat</th>
                </tr>
            </thead>
        <tbody>';
        while( $row = mysql_fetch_assoc($sq) )
          echo "<tr>
          <td>{$row['Absenta']}</td>
          <td>{$row['Materie']}</td>
          <td>{$row['Motivat']}</td>
        </tr>";
        echo'
        </tbody>
    </table>';
    */
    }
    else{
        $sql= mysql_query("SELECT * FROM `Profesori` WHERE `IdProf` = '$username' AND `Password` = '$password'");
        if(mysql_num_rows($sql) > 0)
        {
            $k=mysql_query("SELECT * FROM `Profesori` WHERE `sex`='M' AND `IdProf` = '$username' AND `Password` = '$password'");
            if(mysql_num_rows($k) > 0){
                echo ("<SCRIPT LANGUAGE='JavaScript'>
                window.alert('Bine ati venit domnule ".$z."')
                window.location.href='login1.php'
                </SCRIPT>");
            }
            else{
                echo ("<SCRIPT LANGUAGE='JavaScript'>
                    window.alert('Bine ati venit doamna ".$z."')
                    window.location.href='login1.php'
                    </SCRIPT>");
            }
        }
        else{
            $sql= mysql_query("SELECT * FROM `Diriginte` WHERE `Id` = '$username' AND `Password` = '$password'");
            if(mysql_num_rows($sql) > 0)
            {
                echo ("<SCRIPT LANGUAGE='JavaScript'>
            window.alert('Bine ati venit domnule ".$z."')
            window.location.href='login1.php'
            </SCRIPT>");
            }
            else {
                echo ("<SCRIPT LANGUAGE='JavaScript'>
            window.alert('Nume de utilizator sau parola gresite. Va rugam reintroduceti.')
            window.location.href='login.php'
            </SCRIPT>");
            }
        }
    }
}
?>

sql_connect.php文件用于发布到serv和数据库的连接我必须提到的是，代码是在分部的HTML格式文件中编写的，尽管我认为这不会影响php脚本。这是页面格式化的代码：

<style>
header {
    background-color:white;
    color:white;
    height:5%;
    width:80%;
    float:left;
    text-align:center;
}
details {
    background-color:#B0B0B0;
    color:white;
    height:15%;
    width:80%;
    font-size:180%;
    font-family: "Magneto";
    float:left;
    text-align:center;
}
nav {
    line-height:30px;
    background-color:white;
    height:100%;
    width:10%;
    float:left;
}
section {
    background-color:#F0F0F0 ;
    width:20%;
    height:60%;
    text-align:center;
    float:left;
}
aside {
    background-color:#F0F0F0;
    width:40%;
    height:60%;
    font-family: "High Tower Text";
    text-align:center;
    float:left;
}
summary{
    background-color:#F0F0F0;
    width:20%;
    height:60%;
    text-align:left;
    float:left;
}
article {
    background-color:#B0B0B0;
    color:white;
    text-align:center;
    font-family:'Copperplate Gothic Bold';
    height:15%;
    width:80%;  
    float:left;
}
background-color:red;
</style>  

td；lr变量在运行"if"命令后正在解除准备。

编辑：已解决问题。原来是由于window.location.href='login1.php'命令重新加载了页面