php怎么进行数据库查询和修改操作

$servername = "localhost"; // 数据库主机名$username = "username"; // 数据库用户名$password = "password"; // 数据库密码$dbname = "myDB"; // 数据库名// 创建连接$conn = new mysqli($servername, $username, $password, $dbname);// 检查连接是否成功if ($conn->connect_error) {    die("连接失败: " . $conn->connect_error);}echo "连接成功";

$sql = "SELECT id, name, email FROM users WHERE age > 18";$result = $conn->query($sql);if ($result->num_rows > 0) {    // 输出数据    while($row = $result->fetch_assoc()) {        echo "id: " . $row["id"]. " - Name: " . $row["name"]. " - Email: " . $row["email"]. "<br>";    }} else {    echo "0 结果";}

$sql = "SELECT id, name, email FROM users WHERE age > 18 AND gender = 'female'";$result = $conn->query($sql);

$sql = "UPDATE users SET name='New Name' WHERE id=1";if ($conn->query($sql) === TRUE) {    echo "数据更新成功";} else {    echo "数据更新失败: " . $conn->error;}

$sql = "DELETE FROM users WHERE id=1";if ($conn->query($sql) === TRUE) {    echo "数据删除成功";} else {    echo "数据删除失败: " . $conn->error;}