一、SQL注入实例
后台的插入语句代码：
$unsafe_variable = $_POST['user_input'];
mysql_query("INSERT INTO `table` (`column`) VALUES ('$unsafe_variable')");
当POST的内容为：
value'); DROP TABLE table;--
以上的整个SQL查询语句变成：
INSERT INTO `table` (`column`) VALUES('value'); DROP TABLE table;--')
二、防止SQL注入措施
1.使用预处理语句和参数化查询。（‘Use prepared statements and parameterized queries.’）
SQL语句和查询的参数分别发送给数据库服务器进行解析。这种方式有2种实现：
（1）使用PDO（PHP data object）
$stmt = $pdo->prepare('SELECT * FROM employees WHERE name = :name');
$stmt->execute(array('name' => $name));
foreach ($stmt as $row) {
// do something with $row
}
（2）使用MySQLi
$stmt = $dbConnection->prepare('SELECT * FROM employees WHERE name = ?'); $stmt->bind_param('s', $name);
$stmt->execute();
$result = $stmt->get_result();
while ($row = $result->fetch_assoc()) {
// do something with $row }
2.对查询语句进行转义（最常见的方式）
$unsafe_variable = $_POST["user-input"];
$safe_variable = mysql_real_escape_string($unsafe_variable);
mysql_query("INSERT INTO table (column) VALUES ('" . $safe_variable . "')");
$mysqli = new mysqli("server", "username", "password", "database_name");
// TODO - Check that connection was successful.
$unsafe_variable = $_POST["user-input"];
$stmt = $mysqli->prepare("INSERT INTO table (column) VALUES (?)");
// TODO check that $stmt creation succeeded
// "s" means the database expects a string
$stmt->bind_param("s", $unsafe_variable);
$stmt->execute();
$stmt->close();
$mysqli->close();
3.限制引入的参数
$orders = array("name","price","qty"); //field names
$key = array_search($_GET['sort'],$orders)); // see if we have such a name
$orderby = $orders[$key]; //if not, first one will be set automatically. smart enuf :)
$query = "SELECT * FROM `table` ORDER BY $orderby"; //value is safe
4.对引入参数进行编码
SELECT password FROM users WHERE name = 'root' --普通方式
SELECT password FROM users WHERE name = 0x726f6f74 --防止注入
SELECT password FROM users WHERE name = UNHEX('726f6f74') --防止注入
set @INPUT = hex("%实验%");
select * from login where reset_passwd_question like unhex(@INPUT) ;
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