mysql正反单引号

INSERT INTO users (name, email) VALUES ('John Doe', 'john.doe@example.com');
SELECT * FROM users WHERE name = 'Jane Smith';

SELECT `user_id`, `username` FROM `users`;
CREATE TABLE `user_profiles` (
    `profile_id` INT AUTO_INCREMENT PRIMARY KEY,
    `user_id` INT,
    `bio` TEXT
);

// 不安全的做法
$query = "SELECT * FROM users WHERE username = '" . $_POST['username'] . "'";

// 安全的做法
$username = mysqli_real_escape_string($conn, $_POST['username']);
$query = "SELECT * FROM users WHERE username = '$username'";

$stmt = $conn->prepare("SELECT * FROM users WHERE username = ?");
$stmt->bind_param("s", $_POST['username']);
$stmt->execute();

SELECT `select` FROM `table_with_special_chars`;