php - 检查用户名是否存在sql和php中的代码

Question

我写了一段代码来检查用户名是否存在于数据库中。似乎返回不存在这样的用户名，即使存在相同的用户名也是如此。

$conu=mysqli_connect("localhost","db_user","db_pass","db_name");
$result = mysql_query("SELECT 1 FROM member WHERE username = $username");
if ($result && mysql_num_rows($result) > 0) {
$user_err = "<i><span class='error'>Usernme already exists</span></i>";
    $errflag = true;
}
elseif(preg_match("/^[0-9a-zA-Z_]{5,}$/", $username) === 0) {
    $user_err = "<i><span class='error'>Usernme must be bigger than 5 chararacters and can contain only digits, letters and underscore</span></i>";
    $errflag = true;
}

Answer 1

尝试

mysql_query("SELECT username FROM member WHERE username = '$username' LIMIT 1;");

SELECT 1 实际上并没有使用数据库；它始终返回 1，因此无论 member 表的内容如何，​​您的结果始终相同。