PHP MySQL-如何创建数据库？当前错误：未选择任何数据库

我学习了一门课程的教程，但我一直收到错误消息：

Error creating table: No database selected

我是一个初学者，我不确定我为什么会犯这个错误，以及如何解决它——提前谢谢

<?php

$servername = "localhost";

$conn = mysqli_connect($servername);
mysqli_select_db($conn,"myDB");

if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

$sql = "CREATE TABLE IF NOT EXISTS muq
        (   muqUD INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
            dateTime DATETIME,
            taskTime FLOAT(4,2),
            useTime VARCHAR(60),
            usedM VARCHAR(40),
            freqRate VARCHAR(200),
            gender CHAR(1),
            age TINYINT UNSIGNED,
            email VARCHAR(100),
            comment VARCHAR(3000))          
        ";

if (mysqli_query($conn, $sql)) {
    echo "Table muq created successfully";
} else {
    echo "Error creating table: " . mysqli_error($conn);
}

mysqli_close($conn);
?>

---

在一行中创建连接，如下所示

$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

// Create connection
$conn = mysqli_connect($servername, $username, $password, $dbname);
// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

---

如果需要密码，您没有为它包含用户名（和密码）。如果不是必需的，它仍然应该是一个空参数。如果您的查询已解决，请接受有用的答案