Untitled

<?php
session_start();
if((!isset($_SESSION['login'])) and (!isset($_SESSION['senha']))){
	unset($_SESSION['login']);
	unset($_SESSION['senha']);
	header('location:index.php');
	}
//---------------------
$erro = 0;
?>
<html>
	<head>
		<title>Alterar matéria</title>
		<link rel="shortcut icon" href="imagens\senai.png">
		<link rel="stylesheet" href="css/aluno.css" type="text/css">
	</head>
	<body>
		<div class="tudo">
			<div class="direita">
				<form action="alterarmateria.php" method="post">
					<?php
					include('conexao.php');

						$varsql = "select ds_materia,id_materia from tb_materia order by ds_materia";
						$query = mysql_query($varsql);

						print '<label>Materia:</label><select name="materia">';
						print '<option value="selecione">Selecione</option>';
						while($dados = mysql_fetch_array($query)){
							print " <option value='".$dados['id_materia']."'> ".$dados['ds_materia']." </option> \n";
						}
						print '</select>';
						//-------------------------------------
						if(isset($_POST['materia'])){
						if($_POST['materia'] == 'selecione'){
								echo "<p class='erro'>Selecione a matéria</p>";
								$erro++;
						}
						}
						?>
						<br>
						<br>
					<input type="submit" value="Exluir">
				</form>
			</div>
		</div>
	</body>
</html>
<?php
if(isset($_POST['materia'])){
	if($erro<1){
		include "conexao.php";
		$sql10 = "select id_professor_materia from tb_professor_materia where id_materia = '".$_POST['materia']."'";
		$sql11 = mysql_query($sql10);
		$sql12 = mysql_fetch_array($sql11);
		//----------------------------------------------
		$sql9 = "delete from tb_professor_materia where id_professor_materia = '".$sql12['id_professor_materia']."'";
		$sql13 = mysql_query($sql9);
		//banco
		$sql1 = "delete from tb_materia where id_materia = '".$_POST['materia']."'";
		$sql2 = mysql_query($sql1);
		//---------------------------------
		$query = "select * from tb_materia where id_materia = '".$_POST['materia']."'";
		$sql3 = mysql_query($query);
			if(mysql_num_rows($sql3)==0){
				echo "<script>alert('Matéria excluida com sucesso'); location.href='alterarmateria.php';</script>";
			}else{
				echo "<script>alert('Falhou'); location.href='alterarmateria.php';</script>";
			}
	}
}
?>