如何在PHP中使用数据库查询语言来处理和操作数据库相关的数据类型

<?php
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "myDB";

// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);

// 检测连接
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}
echo "连接成功";
?>

<?php
$sql = "INSERT INTO users (username, password, email) VALUES ('john', '123456', 'john@example.com')";

if ($conn->query($sql) === true) {
    echo "数据插入成功";
} else {
    echo "数据插入失败: " . $conn->error;
}

$conn->close();
?>

<?php
$sql = "SELECT id, username, email FROM users";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    while ($row = $result->fetch_assoc()) {
        echo "ID: " . $row["id"] . " - 用户名: " . $row["username"] . " - 邮箱: " . $row["email"] . "<br>";
    }
} else {
    echo "0 结果";
}

$conn->close();
?>

<?php
$sql = "UPDATE users SET password='654321' WHERE username='john'";

if ($conn->query($sql) === true) {
    echo "数据更新成功";
} else {
    echo "数据更新失败: " . $conn->error;
}

$conn->close();
?>

<?php
$sql = "DELETE FROM users WHERE username='john'";

if ($conn->query($sql) === true) {
    echo "数据删除成功";
} else {
    echo "数据删除失败: " . $conn->error;
}

$conn->close();
?>