Mysqli_query SELECT 返回 false

Question

我目前正在尝试根据学号和密码获取某个用户...问题是 mysqli_query 不断返回 false(?) 语句。 虽然我通过在 PHPMyAdmin 中测试来检查查询。 这是我的查询：

$number = $_POST['number'];
$password = $_POST['password'];

$sql = "SELECT studentNumber FROM student where studentNumber = '$number'" ;
$result = mysqli_query($conn, $sql) or die(mysqli_error());;

if(!$result){
    echo "FAIL";
}
else if($result > 0){
    header("register.html");    
}else{
    $sql = "INSERT INTO 'sampleDB'.'student'('userID', 'studentNumber', 'password') VALUES ('', $number, $password)";
    header("login.html");
}

这是我的代码连接部分：

$conn = new mysqli($servername, $username, $password);

// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

Answer 1

您应该通过num_rows检查查询结果确实产生了多少行，然后如果为零则进行一些插入。

请注意，列引号实际上是反引号而不是单引号：

$number = $_POST['number'];
$password = $_POST['password'];

// checking

$sql = 'SELECT studentNumber FROM student WHERE studentNumber = ?';
$select = $conn->prepare($sql);
$select->bind_param('s', $number);
$select->execute();
// if there is no student number, register
if($select->num_rows > 0) {
    // there is student number found
    header('Location: index.html'); exit;

} else {

    // there is NO student number found
    $sql = 'INSERT INTO sampleDB.student(userID, studentNumber, password) VALUES (NULL, ?, ?)';
    $insert = $conn->prepare($sql);
    $insert->bind_param('ss', $number, $password);
    $insert->execute();

    header('Location: login.html');
}

旁注：您的连接代码似乎在问题上被截断了。 不要忘记将您的数据库名称添加到连接中：

$conn = new mysqli($servername, $username, $password, $database_name);

Answer 2

$sql = "SELECT studentNumber FROM student where studentNumber = '$number'" ;

改成

$sql = "SELECT studentNumber FROM student where studentNumber = '".$number."'" ;

Answer 3

首先获取结果并在您的条件下使用它。

$result2 = mysql_fetch_array($result);