Login PHP sesion

<?php
if(isset($_POST["Login"])){
    $usr=$_POST["user"];
    $pas=$_POST["pass"];

            if(cekSiswa($usr,$pas)>0){}
            elseif(cekGuru($usr,$pas)>0){}
            elseif(cekAdmin($usr,$pas)>0){}
                else{
                    session_destroy();
                    echo "<script>alert('Otentikasi Login GAGAL !,Silakan cek data Anda kembali...');
                    document.location.href='index.php?mnu=login';</script>";
                }

}

function cekAdmin($usr,$pas){
    $ada=0;
    $sa="select * from `tb_admin` where `username`='$usr' and `password`='$pas' and `status`='Aktif'";
                $qa=mysql_query($sa);
                if(mysql_num_rows($qa)>0){
                    $da=mysql_fetch_array($qa);
                    $nama=$da["username"];
                    $kode=$da["kode_admin"];
                    $_SESSION["cnama"]=$nama;
                    $_SESSION["cid"]=$kode;
                    $_SESSION["cstatus"]="Administrator";
        echo "<script>alert('Otentikasi ".$_SESSION["cstatus"]." ".$_SESSION["cnama"]." (".$_SESSION["cid"].") berhasil Login!');
                    document.location.href='index.php?mnu=home';</script>";
                    $ada=1;
                    }
        return $ada;
    }

function cekGuru($usr,$pas){
    $ada=0;
    $sa="select * from `tb_guru` where `username`='$usr' and `password`='$pas' and `status`='Aktif'";
                $qa=mysql_query($sa);
                if(mysql_num_rows($qa)>0){
                    $da=mysql_fetch_array($qa);
                    $nama=$da["nama_guru"];
                    $kode=$da["kode_guru"];
                    $_SESSION["cnama"]=$nama;
                    $_SESSION["cid"]=$kode;

                    $sd="select * from `tb_kelas` where kode_guru='$kode_guru'";
    $qd=mysql_query($sd);
    if(mysql_num_rows($qa)>0){
            $dd=mysql_fetch_array($qd);
                $kode_kelas=$dd["kode_kelas"];
                    $_SESSION["cstatus"]="Wali Kelas";
                    $_SESSION["ckelas"]=$kode_kelas;
        }
    else{
            $_SESSION["cstatus"]="Guru";
        }

        echo "<script>alert('Otentikasi ".$_SESSION["cstatus"]." ".$_SESSION["cnama"]." (".$_SESSION["cid"].") berhasil Login!');
                    document.location.href='index.php?mnu=home';</script>";
                    $ada=1;
                    }
        return $ada;
    }

function cekSiswa($usr,$pas){
    $ada=0;
    $sa="select * from `tb_siswa` where `username`='$usr' and `password`='$pas' ";
                $qa=mysql_query($sa);
                if(mysql_num_rows($qa)>0){
                    $da=mysql_fetch_array($qa);
                    $nama=$da["nama_siswa"];
                    $kode=$da["kode_siswa"];
                    $_SESSION["cnama"]=$nama;
                    $_SESSION["cid"]=$kode;
                    $_SESSION["cstatus"]="Siswa";
        echo "<script>alert('Otentikasi ".$_SESSION["cstatus"]." ".$_SESSION["cnama"]." (".$_SESSION["cid"].") berhasil Login!');
                    document.location.href='index.php?mnu=home';</script>";
                    $ada=1;
                    }
        return $ada;
    }
?>
<?php


?>