MySQL：没有数据库选择错误

Question

嗨我有一个sql错误说：没有数据库选择这是我的KK.php文件：

$user_name = "root";
$password = "";
$database = "MyDB";
$server = "localhost";

// Check connection
if (mysqli_connect_errno()) {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}

// escape variables for security
$message = mysqli_real_escape_string($link, $_POST['input1']);

$sql="INSERT INTO demo (message)
VALUES ('$message')";

if (!mysqli_query($link,$sql)) {
die('Error: ' . mysqli_error($link));
 }
echo "1 record added";

 mysqli_close($link);
 ?> 

我的数据库是“MyDB”，还有我的demo.php文件：

<form action="KK.php" method="post" />
<p>Message: <input type="text" name="input1" /></p>
<input type="submit" value="Submit" />
</form>

那么问题是什么？，我如何选择数据库？

Answer 1

您是否忘记调用mysqli_connect来获取连接？

即：

$con = mysqli_connect("localhost","my_user","my_password","my_db");

Answer 2

除了我上面的评论，这里还有你缺少的代码。

$user_name = "root";
$password = "";
$database = "MyDB";
$server = "localhost";

// This
$link = mysqli_connect($server,$user_name,$password,$database); // This
// This

// Check connection
if (mysqli_connect_errno()) {
    echo "Failed to connect to MySQL: " . mysqli_connect_error();
}

Answer 3

您没有致电mysqli_connect

$con = mysqli_connect("localhost","my_user","my_password","my_db");