我正在研究数据库系统,我正在尝试避免重复的电子邮件和用户名条目.我已经尝试但它仍然拒绝,但无法确切地看到被拒绝的内容.谁能告诉我哪里错了？
if(isset($_POST['submit'])){
$username = $_POST['username'];
$password = $_POST['password'];
$email = $_POST['email'];
$sql="INSERT into users (username,password,email) VALUES('$username','$password','$email')";
$result = mysql_query("INSERT INTO users VALUES ('duplicate')");
if (!$result) {
echo "Enter a different value";
} else {
echo "Save successful.";
}
}